Non-cash restructuring charges Restructuring and Related Cost, Accelerated Depreciation Entity Address, City or Town Entity Address, City or Town Schedule of Prepaid and Other Current Assets Schedule of Other Current Assets [Table Text Block] Fair Value Disclosures [Abstract] EARNINGS PER SHARE Earnings Per Share [Abstract] Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Process Optimization Member Process Optimization Member Process optimization [Member] Depreciation Depreciation Not Including Integration Component Depreciation, not including integration component. Net Cash Provided by (Used in) Financing Activities [Abstract] CASH FLOWS USED IN FINANCING ACTIVITIES Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect DECREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH Decrease in cash, cash equivalents and other restricted cash Decrease in cash, cash equivalents and other restricted cash Fair Value Measurement Fair Value Measurement [Domain] Deferred contract costs Capitalized Contract Cost, Net, Current Liabilities for uncertain tax positions Liability for Uncertainty in Income Taxes, Noncurrent Contract with Customer, Performance Obligation Satisfied in Previous Period Contract with Customer, Performance Obligation Satisfied in Previous Period Amendment Flag Amendment Flag Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Finite-lived intangible assets, accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization U.K. Her Majesty's Revenue and Customs (HMRC) [Member] Payments for (Proceeds from) Investments, Total Payments for (Proceeds from) Investments Sale of investments Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Goodwill, Total Goodwill Goodwill, net, beginning balance Goodwill, net, ending balance Goodwill Right-of-use assets Operating Lease, Right-of-Use Asset Changes in the Net Carrying Amount of the Components of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Other Comprehensive Income Location Other Comprehensive Income Location [Axis] March 31 2022 [Member] March Thirty One Two Thousand Twenty Two [Member] March thirty one two thousand twenty two. Disposal Group Name Disposal Group Name [Axis] Debt instrument maturity year Debt Instrument Maturity Year Debt instrument maturity year. Document Quarterly Report Document Quarterly Report Debt Instrument [Table] Schedule of Long-Term Debt Instruments [Table] Payments for Repurchase of Common Stock Repurchase of shares Repurchase of shares Foreign currency translation [Member] Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Cash and Cash Equivalents [Domain] Statement [Table] Statement [Table] Long-term lease liabilities Operating Lease, Liability, Noncurrent Interest on lease liabilities Finance Lease, Interest Expense PRW [Member] Other Postretirement Benefits Plan [Member] Litigation Status Litigation Status [Axis] Number of operating segments Number of Operating Segments Service Service [Member] Business Acquisition Business Acquisition [Axis] Accumulated Other Comprehensive Income Loss [Table] Accumulated Other Comprehensive Income (Loss) [Table] Restructuring Charges, Total Restructuring Charges Restructuring costs Charges incurred Restructuring costs Dividends paid Payments of Ordinary Dividends, Common Stock Effect on Future Cash Flows, Amount Restructuring, Expected future effects 5.750% senior notes due 2021 [Member] Senior Notes Due202105750 [Member] Senior notes due 2021, 05750. Preliminary pre-tax gain on sale Tax exempt gain on sale Preliminary pre-tax gain on sale Net loss/(gain) on disposal of operations Adjustment to gain on disposal of Willis Re Nature of Operations Nature of Operations [Text Block] Hedging Relationship Hedging Relationship [Domain] Product and Service Product and Service [Axis] BDA [Member] Benefits Delivery And Administration [Member] Benefits delivery and administration. Business Combination, Contingent Consideration, Liability, Total Business Combination, Contingent Consideration, Liability Acquisitions, contingent consideration Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax) Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Weighted average remaining life of amortizable intangible assets Finite-Lived Intangible Asset, Useful Life Stock Options [Member] Share-Based Payment Arrangement, Option [Member] Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture, Total Issuance of shares under employee stock compensation plans (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Accounts receivable, net balances excluded from held-for-sale Accounts Receivable Net Balances Excluded From Held For Sale Accounts receivable, net balances excluded from held-for-sale. TOTAL LIABILITIES AND EQUITY Liabilities and Equity AOCL [Member] AOCI Including Portion Attributable to Noncontrolling Interest [Member] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Gain/(loss) reclassified from Accumulated OCL into income (effective element) Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net, Total Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Pension benefits assets Assets for Plan Benefits, Defined Benefit Plan Other current liabilities Other Liabilities, Current Total other non-current liabilities Accumulated impairment losses, beginning balance Accumulated impairment losses, ending balance Goodwill, Impaired, Accumulated Impairment Loss Unbilled Receivable, Current Unbilled Receivables, Current Deferred tax expense Deferred Foreign Income Tax Expense (Benefit) Fair Value Inputs, Discount Rate [Member] Measurement Input, Discount Rate [Member] Merger-Related Securities Litigation [Member] Willis Towers Watson Merger Related Securities Litigation [Member] Willis Towers Watson merger-related securities litigation. Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Income Statement [Abstract] Contingent consideration Obligations, Fair Value Disclosure Derivative Liability, Total Derivative financial instruments Derivative liability, fair value Derivative Liability Operating Segments [Member] Operating Segments [Member] Salaries and benefits Labor and Related Expense Total current liabilities Liabilities, Current Contract with Customer, Asset, after Allowance for Credit Loss, Current, Total Contract asset, Current Contract with Customer, Asset, after Allowance for Credit Loss, Current Loss Contingency Nature Loss Contingency Nature [Axis] Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent, Total Contract asset, Noncurrent Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent Other Income, Net [Member] Other Income [Member] Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest, Total Comprehensive income attributable to non-controlling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Business Acquisition, Acquiree Business Acquisition, Acquiree [Domain] Recurring [Member] Fair Value, Recurring [Member] Interest Expense, Total Interest expense Interest Expense Accounts Receivable, Allowance for Credit Loss, Ending Balance Accounts Receivable, Allowance for Credit Loss, Beginning Balance Allowance for doubtful debts Accounts Receivable, Allowance for Credit Loss Real estate rationalization. Real estate rationalization [Member] Real Estate Rationalization [Member] Short-term lease cost Short-Term Lease, Cost Willis Towers Watson Public Limited Company [Member] Willis Towers Watson Public Limited Company [Member] Willis Towers Watson public limited company. Preference shares, shares authorized Preferred Stock, Shares Authorized Reclassification from AOCI, Current Period, Tax, Total Reclassification from AOCI, Current Period, Tax Reclassification from AOCI, Current Period, Tax Fiduciary liabilities Fiduciary Liabilities Current Fiduciary liabilities, current. Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Income from continuing operations attributable to WTW Income from continuing operations attributable to WTW 3.600% senior notes due 2024 [Member] Senior Notes Due202403600 [Member] Senior notes due 2024, 03600. Treasury Stock, Shares, Ending Balance Treasury Stock, Shares, Beginning Balance Treasury Stock, Shares, Total Treasury shares Treasury Stock, Shares Derivative Asset, Total Derivative financial instruments Derivative assets, fair value Derivative Asset Corporate, Non-Segment Corporate, Non-Segment [Member] Entity Small Business Entity Small Business Number of reportable segments Number of Reportable Segments Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Total CASH, CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF PERIOD CASH, CASH EQUIVALENTS AND RESTRICTED CASH, END OF PERIOD Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Cash, cash equivalents and restricted cash Hedging Relationship Hedging Relationship [Axis] Restructuring and Related Activities [Abstract] Restructuring Reserve, Total Restructuring Reserve Beginning Balance Ending Balance Divested businesses Divested Businesses Divested businesses Compensation And Retirement Disclosure [Table] Compensation And Retirement Disclosure [Table] Compensation and retirement disclosure. Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases Obligations assumed Consulting [Member] Consulting [Member] Consulting. Total current assets Assets, Current Trademark and trade name [Member] Trademarks and Trade Names [Member] Increase (Decrease) in Other Operating Liabilities, Total Other liabilities Increase (Decrease) in Other Operating Liabilities Effect on Future Earnings, Amount Annual cost savings of program Weighted Average Number of Shares Outstanding, Basic, Total Basic average number of shares outstanding (shares) Weighted Average Number of Shares Outstanding, Basic Health Wealth Career Segment . Health Wealth Career Segment [Member] HWC [Member] Schedule of Other Non-current Liabilities Other Noncurrent Liabilities [Table Text Block] City Area Code City Area Code Schedule of Current and Long-term Debt Schedule of Debt [Table Text Block] Acquisitions and Divestitures Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Schedule of Net Periodic Benefit Cost Schedule of Net Benefit Costs [Table Text Block] Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net, Total Loss recognized in income Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Accumulated Other Comprehensive Loss Comprehensive Income (Loss) Note [Text Block] Schedule of Other Nonoperating Income Schedule of Other Nonoperating Income (Expense) [Table Text Block] TOTAL LIABILITIES Liabilities Document Period End Date Document Period End Date Business Combination and Asset Acquisition [Abstract] Schedule Of Finite Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Fiduciary assets Funds Held for Clients Entity Number of Employees Number of employees employed (more than 46,000) Delaware Action [Member] Delaware Action [Member] Delaware Action. Other [Member] Product and Service, Other [Member] Net periodic benefit (income)/cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Intangible asset disposals Finite Lived Intangible Assets Disposed Finite-lived intangible assets disposed. Software [Member] Software and Software Development Costs [Member] Finite-Lived Intangible Asset, Expected Amortization, Year One 2023 Cash and fiduciary funds transferred in sale of operations Cash Divested from Deconsolidation Statistical Measurement Statistical Measurement [Axis] HCB [Member] Human Capital And Benefits [Member] Human capital and benefits. Foreign currency translation Adjustments To Additional Paid In Capital Foreign Currency Translation Gain Loss Adjustments to additional paid in capital, foreign currency translation gain (loss). Other current assets Other Assets, Current Additions to fixed assets and software for internal use Payments To Acquire Fixed Assets And Software For Internal Use Payments to acquire fixed assets and software for internal use. Restructuring Costs, Total Restructuring Costs Total Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance Stockholders' Equity Attributable to Noncontrolling Interest, Beginning Balance Stockholders' Equity Attributable to Noncontrolling Interest, Total Non-controlling interests Stockholders' Equity Attributable to Noncontrolling Interest Balance Sheet Date Balance Sheet Date [Domain] Balance sheet date. TOTAL ASSETS Assets Minority Interest [Line Items] Noncontrolling Interest [Line Items] Derivative Contract Derivative Contract [Domain] Previously Reported [Member] Costs of providing services Costs and Expenses [Abstract] Derivative [Line Items] Derivative [Line Items] Western Europe [Member] Western Europe [Member] Western Europe. Senior notes issued Proceeds from Issuance of Senior Long-Term Debt Long-term Debt, Excluding Current Maturities, Total Long-term debt, excluding current maturities Long-term debt Long-Term Debt, Excluding Current Maturities Diluted earnings per share Diluted earnings per share Earnings Per Share, Diluted Retirement Plan Type Retirement Plan Type [Axis] Corporate income and other taxes Income Taxes Receivable, Current Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block] Balance as of beginning of period Balance as of end of period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Discontinued Operations [Member] Discontinued Operations [Member] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Total costs of providing services Disposal Group Including Discontinued Operation Costs Of Providing Services Disposal group including discontinued operation costs of providing services. Earnings Per Share, Basic [Abstract] Basic earnings per share: Revision of Prior Period [Axis] Document Fiscal Period Focus Document Fiscal Period Focus Accounts payable, accrued liabilities and deferred income Accounts Payable, Other, Current Accounts receivable Increase (Decrease) in Accounts Receivable Pension Plan [Member] Pension Plan [Member] Revolving Credit Facility [Member] Revolving Credit Facility [Member] Derivative [Table] Derivative [Table] Goodwill disposals Goodwill, Written off Related to Sale of Business Unit Other Income, Net Other Income and Other Expense Disclosure [Text Block] Counterparty Name Counterparty Name [Domain] Capitalized software costs Payments to Develop Software Rollforward of liability associated with cash-based charges. Rollforward of liability associated with cash-based charges [Table Text Block] Rollforward of Liability Associated with Cash-based Charges Net Cash Provided by (Used in) Financing Activities Net cash used in financing activities Statement of Financial Position [Abstract] Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Realized and unrealized losses Entity File Number Entity File Number Disposal Groups, Including Discontinued Operations [Table Text Block] Schedule of Selected Financial Information (Loss)/income from discontinued operations per share Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share Statement of Cash Flows [Abstract] Noncontrolling Interest, Increase from Business Combination Acquisition of non-controlling interests Willis Re [Member] Willis Re [Member] Willis Re. Sublease income Sublease Income Deferred Revenue Arrangement Type [Axis] Retirement Benefits Retirement Benefits [Text Block] Error Corrections and Prior Period Adjustments Restatement [Line Items] Geographical Geographical [Domain] Unallocated, net Other Operating Income (Expense), Net Statistical Measurement Statistical Measurement [Domain] Statement of Stockholders' Equity [Abstract] Dilutive effect of potentially issuable shares, continuing operations (USD per share) Dilutive Securities Effect On Basic Earnings Per Share Continuing Operations Dilutive securities effect on basic earnings per share continuing operations. Dilutive effect of potentially issuable shares Class of Stock Class of Stock [Domain] Revenue, Percentage of Total Revenue Individual Revenue Streams Percentage Of Total Revenue Individual revenue streams percentage of total revenue. Deferred compensation plan assets Deferred Compensation Plan Assets Current Deferred compensation plan assets current. Stock Repurchased and Retired During Period, Shares Shares repurchased (in shares) Schedule of Lease Costs Recorded in Condensed Consolidated Statements of Comprehensive Income Lease, Cost [Table Text Block] Fair Value Measurements Fair Value Disclosures [Text Block] Disposal Group, Including Discontinued Operation, Liabilities, Current, Total Disposal Group, Including Discontinued Operation, Liabilities, Current Current liabilities held for sale Proceeds from issuance of shares Proceeds from Issuance of Common Stock Long-Term Debt, Type [Axis] Deferred Income Tax Expense (Benefit), Total Deferred Income Tax Expense (Benefit) (Benefit from)/provision for deferred income taxes Revenue [Member] Revenue [Member] Revenue member. Weighted Average Number Diluted Shares Outstanding Adjustment, Total Dilutive effect of potentially issuable shares (shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment Deferred Income Tax Liabilities, Net, Total Deferred tax liabilities Deferred Income Tax Liabilities, Net Revenue Revenue from Contract with Customer [Text Block] Antidilutive Securities Antidilutive Securities [Axis] Disposal Group, Including Discontinued Operation, Revenue Revenue from discontinued operations Longest outstanding maturity Derivative, Remaining Maturity Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Sale of non-controlling interests Noncontrolling Interest, Increase from Sale of Parent Equity Interest Preference shares, nominal value (USD per share) Preferred Stock, Par or Stated Value Per Share Loss Contingency, Nature Loss Contingency, Nature [Domain] Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year Remainder of 2022 Lessee, Lease, Description [Line Items] 4.650% senior notes due 2027 [Member] Senior Notes Due 202704650 [Member] Senior notes due 202704650 [Member]. Supplementary Information for Certain Balance Sheet Accounts Supplemental Balance Sheet Disclosures [Text Block] Credit Facility Credit Facility [Domain] Not Designated as Hedging Instrument [Member] Nondesignated [Member] Not Designated as Hedging Instrument [Member] Diluted average number of shares outstanding (shares) Weighted Average Number of Shares Outstanding, Diluted Diluted average number of shares outstanding (shares) Retirement Plan Sponsor Location Retirement Plan Sponsor Location [Domain] Finite-Lived Intangible Assets, Major Class Name Finite-Lived Intangible Assets, Major Class Name [Domain] Credit Facility Credit Facility [Axis] Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Portion at Fair Value Measurement [Member] [Default] Fair Value Disclosure Item Amounts [Default] Portion at Fair Value Measurement [Member] Broking [Member] Broking [Member] Broking. Earnout receivable in cash in 2025 Earnout Receivable In Cash Earnout receivable in cash not recognized as an asset on balance sheet. Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Supplemental Disclosures Regarding Cash Flow Information and Non-cash Flow Investing and Financing Activities Aon Plc [Member] Aon Plc [Member] Aon plc. Current Fiscal Year End Date Current Fiscal Year End Date Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax, Total Reclassifications of foreign currency translation Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax Derivative Instruments and Hedging Activities Disclosure [Abstract] Liability Class Liability Class [Axis] Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Total Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax (Loss)/gain recognized in OCI (effective element) Depreciation, Total Depreciation Depreciation Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Beginning Balance Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Ending Balance Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Total cash, cash equivalents and restricted cash Total cash, cash equivalents and restricted cash Stock Repurchased and Retired During Period, Value Shares repurchased Other Assets, Noncurrent, Total Other non-current assets Other Assets, Noncurrent Total equity Equity, beginning balance Equity, ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Entity Address, Address Line One Entity Address, Address Line One Repayments of Long-term Debt, Total Repayments of debt Repayments of Long-Term Debt Schedule of Derivative Instruments Designated/Nondesignated As Hedging Instrument Effect on Condensed Consolidated Statements of Comprehensive Income Derivative Instruments, Gain (Loss) [Table Text Block] Non-controlling interests [Member] Noncontrolling Interest [Member] Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Finite-Lived Intangible Assets by Major Class Finite-Lived Intangible Assets by Major Class [Axis] Supplemental Cash Flow Information [Abstract] Supplemental disclosures of cash flow information: Ordinary shares and APIC [Member] Common Stock Including Additional Paid in Capital [Member] (Loss)/income from discontinued operations per share Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share Income Tax Expense (Benefit), Total Provision for income taxes Provision for income taxes Income Tax Expense (Benefit) Contingent consideration [Member] Obligations [Member] Fiduciary liabilities excluded from held for sale. Fiduciary liabilities excluded from held for sale Senior Notes [Member] Senior Notes [Member] Income Taxes Income Tax Disclosure [Text Block] Preferred Stock, Shares Issued, Total Preference shares, shares issued Preferred Stock, Shares Issued Balance Sheet Location [Domain] Segment Reporting Reconciling Item For Operating Profit Loss From Segment To Consolidated [Line Items] Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] Foreign exchange contracts [Member] Foreign Exchange Contract [Member] Other non-current liabilities Other Sundry Liabilities, Noncurrent Revenue, Remaining Performance Obligation Revenue, Remaining Performance Obligation, Amount Income Tax Disclosure [Abstract] Schedule of Liabilities Whose Carrying Values Differ From the Fair Value and are Not Measured on a Recurring Basis Fair Value Measurements, Nonrecurring [Table Text Block] Dilutive effect of potentially issuable shares Dilutive Securities Effect On Basic Earnings Per Share Discontinued Operations Dilutive securities effect on basic earnings per share discontinued operations. Dilutive effect of potentially issuable shares Non-Fiduciary. Non-Fiduciary [Member] Carrying Value [Member] Reported Value Measurement [Member] Assets: Assets, Fair Value Disclosure [Abstract] Total costs of providing services Costs and Expenses Fair Value Hierarchy and NAV Fair Value Hierarchy and NAV [Axis] 4.400% senior notes due 2026 [Member] Senior Notes Due202604400 [Member] Senior notes due 2026, 04400. 4.625% senior notes due 2023 [Member] Senior Notes Due202304625 [Member] Senior notes due 2023, 04625. Goodwill and Intangible Assets Disclosure [Abstract] Amortization of prior service credit Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Certificates of deposit and term deposits. Certificates of Deposit And Term Deposits [Member] Transaction and integration expenses Business Combination Integration Related Transaction Costs Business combination integration related transaction costs. Transaction and transformation, net Transaction and transformation, net Equity [Abstract] Contract with Customer, Liability, Revenue Recognized Contract with Customer, Liability, Revenue Recognized Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax Income from discontinued operations before income taxes Income from discontinued operations before income taxes Other Foreign Plans [Member] Other Foreign Plans [Member] Other foreign plans. Income from operations Income from operations Income/(loss) from operations Operating Income (Loss) Stated interest rate Debt Instrument, Interest Rate, Stated Percentage Total non-current liabilities Liabilities, Noncurrent Additional Paid in Capital, Common Stock, Ending Balance Additional Paid in Capital, Common Stock, Beginning Balance Additional paid-in capital Additional Paid in Capital, Common Stock Reimbursable expenses and other Reimbursable Expenses And Other Reimbursable expenses and other. Proposed Combination with AON Plc [Member] Proposed Combination With A O N Plc [Member] Proposed combination with AON plc. Payments to Acquire Businesses, Net of Cash Acquired, Total Acquisitions of operations, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Entity Filer Category Entity Filer Category Cumulative costs. Cumulative Costs [Member] Cumulative Costs [Member] Restructuring Plan [Domain] Long-term debt, excluding current maturities Other Long-Term Debt, Noncurrent Non-cash Revaluation Gain Related to Acquisition [Member] Non-cash revaluation gain related to acquisition. Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Net current-period other comprehensive (loss)/income Fair Value by Liability Class Fair Value by Liability Class [Domain] Entity Current Reporting Status Entity Current Reporting Status Foreign exchange Goodwill, Foreign Currency Translation Gain (Loss) Asset Class [Domain] Book of Business Settlements [Member] Book of business settlements. AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Deferred Revenue and Accrued Expenses Schedule of Accounts Payable and Accrued Liabilities [Table Text Block] Asset Impairment Charges, Total Asset Impairment Charges Impairment Impairment Derivatives and investments Derivatives And Investments Current Derivatives and investments current. Business Combinations [Abstract] Finite-Lived Intangible Assets, Net, Ending Balance Finite-Lived Intangible Assets, Net, Beginning Balance Total Finite-lived intangible assets, net amount Finite-Lived Intangible Assets, Net Earnings Per Share, Diluted [Abstract] Diluted earnings per share: Stockholders' equity attributable to parent, beginning balance Stockholders' equity attributable to parent, ending balance Stockholders' Equity Attributable to Parent Total WTW shareholders equity Net proceeds/(payments) from fiduciary funds held for clients Net (payments)/proceeds from fiduciary funds held for clients. Net Payments Proceeds from Fiduciary Funds Held for Clients Net (payments)/proceeds from fiduciary funds held for clients Total [Member] AOCI Attributable to Parent [Member] Asset Class [Axis] Entity Tax Identification Number Entity Tax Identification Number Income Statement Location Income Statement Location [Axis] Consolidation Items Consolidation Items [Axis] Retained Earnings (Accumulated Deficit), Ending Balance Retained Earnings (Accumulated Deficit), Beginning Balance Retained Earnings (Accumulated Deficit), Total Retained earnings Retained Earnings (Accumulated Deficit) Equity Components Equity Components [Axis] 6.125% senior notes due 2043 [Member] Senior Notes Due204306125 [Member] Senior notes due 2043, 06125. Leases [Abstract] Contract with Customer, Liability, Total Deferred revenue Contract with Customer, Liability Client relationships [Member] Customer Relationships [Member] Disaggregation Of Revenue [Table] Disaggregation of Revenue [Table] Entity Emerging Growth Company Entity Emerging Growth Company Interest cost Defined Benefit Plan, Interest Cost Goodwill [Roll Forward] Goodwill [Roll Forward] Income (Loss) from Continuing Operations, Per Diluted Share Income from continuing operations per share Diluted earnings per share from continuing operations attributable to WTW Diluted earnings per share from continuing operations attributable to WTW Gallagher [Member] Gallagher [Member] Gallagher. Goodwill [Line Items] Goodwill [Line Items] Retirement Plan Type Retirement Plan Type [Domain] Other income, net Disposal Group Including Discontinued Operation Other Expense Income Net Disposal group including discontinued operation other expense (income) net. Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Contract with Customer, Asset and Liability Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Diluted (loss)/ earnings per share from discontinued operations, net of tax Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Diluted earnings per share from discontinued operations, net of tax Reduction of non-controlling interests Noncontrolling Interest, Decrease from Deconsolidation Europe [Member] Europe [Member] Service cost Defined Benefit Plan, Service Cost CRB [Member] Corporate Risk And Broking [Member] Corporate risk and broking. Divested Businesses Divested Businesses [Member] Divested Businesses [Member] Gain/(loss) on disposal of operations Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal Retirement Benefits [Abstract] Document Transition Report Document Transition Report Fiduciary assets. Fiduciary Assets [Member] Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest, Total Net income Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Litigation settlements Estimated Litigation Liability, Current Thereafter Finite Lived Intangible Assets Amortization Expense After Year Four Finite lived intangible assets amortization expense after year four. Schedule Of Segment Reporting Information By Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract] Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Outsourced administration [Member] Outsourced Administration [Member] Outsourced administration. Effect of exchange rate changes on cash, cash equivalents and restricted cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Continuing Operations Risk And Uncertainties Policy [Text Block] Risk and uncertainties. Risks and Uncertainties of the Economic Environment Caused by the Pandemic Accumulated Other Comprehensive Income (Loss), Net of Tax, Total Accumulated other comprehensive loss, net of tax Accumulated Other Comprehensive Income (Loss), Net of Tax Accounts receivable, net Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Cash Flow, Supplemental Disclosures [Text Block] Supplemental Disclosures of Cash Flow Information Revision of Prior Period [Domain] 4.500% senior notes due 2028 [Member] Senior Notes Due2028045 [Member] Senior notes due 2028, 045. Net income attributable to Willis Towers Watson Net Income (Loss) Attributable to Parent NET INCOME ATTRIBUTABLE TO WTW Great Britain [Member] Great Britain [Member] Great Britain. Current lease liabilities Operating Lease, Liability, Current Deconsolidation, Gain (Loss), Amount Deconsolidation, Gain (Loss), Amount Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Expected decrease in liability for uncertain tax position Decrease in Unrecognized Tax Benefits is Reasonably Possible Payment, Tax Withholding, Share-Based Payment Arrangement Cash paid for employee taxes on withholding shares Cash paid for employee taxes on withholding shares Line of credit maturity date Line of Credit Facility, Expiration Date Restructuring Plan [Axis] Entity Registrant Name Entity Registrant Name Cash and Cash Equivalents, at Carrying Value, Ending Balance Cash and Cash Equivalents, at Carrying Value, Beginning Balance Cash and Cash Equivalents, at Carrying Value, Total Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Earnings Per Share Earnings Per Share [Text Block] Class of Stock Class of Stock [Axis] Maturity date Debt Instrument, Maturity Date Lessee, Lease, Description [Table] Revenues Total revenue Revenue Revenues Share-based Payment Arrangement, Noncash Expense, Total Share-based compensation Share-Based Payment Arrangement, Noncash Expense Property, Plant and Equipment, Net, Ending Balance Property, Plant and Equipment, Net, Beginning Balance Property, Plant and Equipment, Net, Total Fixed assets, net Property, Plant and Equipment, Net Amortization of right-of-use assets Finance Lease, Right-of-Use Asset, Amortization Award Type Award Type [Domain] Statement [Line Items] Statement [Line Items] Derivative instruments [Member] AOCI, Derivative Qualifying as Hedge, Excluded Component, Parent [Member] Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture, Total Issuance of shares under employee stock compensation plans Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Current portion of long term debt Other Long-Term Debt, Current Liabilities: Liabilities, Fair Value Disclosure [Abstract] (LOSS)/INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX Goodwill, Purchase Accounting Adjustments Acquisition accounting adjustment Title of 12(b) Security Title of 12(b) Security Finite-Lived Intangible Assets, Gross, Total Finite-lived intangible assets, gross carrying amount Finite-Lived Intangible Assets, Gross Ownership Ownership [Domain] Restructuring Cost and Reserve [Line Items] Shares outstanding [Member] Common Stock [Member] Derivative, notional amount Derivative, Notional Amount Net Cash Provided by (Used in) Operating Activities [Abstract] CASH FLOWS FROM/(USED IN) OPERATING ACTIVITIES Equity Component Equity Component [Domain] Revenue from Contract with Customer, Excluding Assessed Tax, Total Revenue from Contract with Customer, Excluding Assessed Tax Revenue from Contract with Customer, Excluding Assessed Tax Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES Income from continuing operations before income taxes 3.875% senior notes due 2049 [Member] Senior Notes Due204903875 [Member] Senior notes due 2049, 03875. 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