100000 - Document - Document and Entity Information link:presentationLink link:calculationLink link:definitionLink 100010 - Statement - Condensed Consolidated Statements of Comprehensive Income (Unaudited) link:presentationLink link:calculationLink link:definitionLink 100020 - Statement - Condensed Consolidated Balance Sheets (Unaudited) link:presentationLink link:calculationLink link:definitionLink 100030 - Statement - Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 100040 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited) link:presentationLink link:calculationLink link:definitionLink 100050 - Statement - Condensed Consolidated Statements of Changes in Equity (Unaudited) link:presentationLink link:calculationLink link:definitionLink 100060 - Statement - Condensed Consolidated Statements of Changes in Equity (Unaudited) (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 100070 - Disclosure - Nature of Operations link:presentationLink link:calculationLink link:definitionLink 100080 - Disclosure - Basis of Presentation link:presentationLink link:calculationLink link:definitionLink 100090 - Disclosure - Acquisitions and Divestitures link:presentationLink link:calculationLink link:definitionLink 100100 - Disclosure - Revenue link:presentationLink link:calculationLink link:definitionLink 100110 - Disclosure - Segment Information link:presentationLink link:calculationLink link:definitionLink 100120 - Disclosure - Restructuring Costs link:presentationLink link:calculationLink link:definitionLink 100130 - Disclosure - Income Taxes link:presentationLink link:calculationLink link:definitionLink 100140 - Disclosure - Goodwill and Other Intangible Assets link:presentationLink link:calculationLink link:definitionLink 100150 - Disclosure - Derivative Financial Instruments link:presentationLink link:calculationLink link:definitionLink 100160 - Disclosure - Debt link:presentationLink link:calculationLink link:definitionLink 100170 - Disclosure - Fair Value Measurements link:presentationLink link:calculationLink link:definitionLink 100180 - Disclosure - Retirement Benefits link:presentationLink link:calculationLink link:definitionLink 100190 - Disclosure - Leases link:presentationLink link:calculationLink link:definitionLink 100200 - Disclosure - Commitments and Contingencies link:presentationLink link:calculationLink link:definitionLink 100210 - Disclosure - Supplementary Information for Certain Balance Sheet Accounts link:presentationLink link:calculationLink link:definitionLink 100220 - Disclosure - Other Income, Net link:presentationLink link:calculationLink link:definitionLink 100230 - Disclosure - Accumulated Other Comprehensive Loss link:presentationLink link:calculationLink link:definitionLink 100240 - Disclosure - Earnings Per Share link:presentationLink link:calculationLink link:definitionLink 100250 - Disclosure - Supplemental Disclosures of Cash Flow Information link:presentationLink link:calculationLink link:definitionLink 100260 - Disclosure - Basis of Presentation (Policies) link:presentationLink link:calculationLink link:definitionLink 100270 - Disclosure - Acquisitions and Divestitures (Tables) link:presentationLink link:calculationLink link:definitionLink 100280 - Disclosure - Revenue (Tables) link:presentationLink link:calculationLink link:definitionLink 100290 - Disclosure - Segment Information (Tables) link:presentationLink link:calculationLink link:definitionLink 100300 - Disclosure - Restructuring Costs (Tables) link:presentationLink link:calculationLink link:definitionLink 100310 - Disclosure - Goodwill and Other Intangible Assets (Tables) link:presentationLink link:calculationLink link:definitionLink 100320 - Disclosure - Derivative Financial Instruments (Tables) link:presentationLink link:calculationLink link:definitionLink 100330 - Disclosure - Debt (Tables) link:presentationLink link:calculationLink link:definitionLink 100340 - Disclosure - Fair Value Measurements (Tables) link:presentationLink link:calculationLink link:definitionLink 100350 - Disclosure - Retirement Benefits (Tables) link:presentationLink link:calculationLink link:definitionLink 100360 - Disclosure - Leases (Tables) link:presentationLink link:calculationLink link:definitionLink 100370 - Disclosure - Supplementary Information for Certain Balance Sheet Accounts (Tables) link:presentationLink link:calculationLink link:definitionLink 100380 - Disclosure - Other Income, Net (Tables) link:presentationLink link:calculationLink link:definitionLink 100390 - Disclosure - Accumulated Other Comprehensive Loss (Tables) link:presentationLink link:calculationLink link:definitionLink 100400 - Disclosure - Earnings Per Share (Tables) link:presentationLink link:calculationLink link:definitionLink 100410 - Disclosure - Supplemental Disclosures of Cash Flow Information (Tables) link:presentationLink link:calculationLink link:definitionLink 100420 - Disclosure - Nature of Operations (Details) link:presentationLink link:calculationLink link:definitionLink 100430 - Disclosure - Acquisitions and Divestitures (Additional Information) (Details) link:presentationLink link:calculationLink link:definitionLink 100440 - Disclosure - Acquisitions and Divestitures - Divestment of Russian Business (Details) link:presentationLink link:calculationLink link:definitionLink 100450 - Disclosure - Acquisitions and Divestitures - Willis Re Divestiture (Details) link:presentationLink link:calculationLink link:definitionLink 100460 - Disclosure - Acquisitions and Divestitures - Schedule of Selected Financial Information Relates to the Operations of Willis Re (Details) link:presentationLink link:calculationLink link:definitionLink 100470 - Disclosure - Acquisitions and Divestitures - Miller Divestiture (Details) link:presentationLink link:calculationLink link:definitionLink 100480 - Disclosure - Acquisitions and Divestitures - Other Disposals (Details) link:presentationLink link:calculationLink link:definitionLink 100490 - Disclosure - Revenue - Schedule of Disaggregation of Revenue (Details) link:presentationLink link:calculationLink link:definitionLink 100500 - Disclosure - Revenue - Schedule of Disaggregation of Revenue (Parenthetical) (Details) link:presentationLink link:calculationLink link:definitionLink 100510 - Disclosure - Revenue - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100520 - Disclosure - Revenue - Schedule of Revenue by Geography (Detail) link:presentationLink link:calculationLink link:definitionLink 100530 - Disclosure - Revenue - Schedule of Contract Balances (Details) link:presentationLink link:calculationLink link:definitionLink 100540 - Disclosure - Revenue - Schedule of Contract Balances (Parenthetical) (Details) link:presentationLink link:calculationLink link:definitionLink 100550 - Disclosure - Revenue - Schedule of Remaining Performance Obligations (Details) link:presentationLink link:calculationLink link:definitionLink 100560 - Disclosure - Revenue - Schedule of Remaining Performance Obligations (Details1) link:presentationLink link:calculationLink link:definitionLink 100570 - Disclosure - Segment Information - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100580 - Disclosure - Segment Information - Revenue (Net of Reimbursable Expenses) of the Reported Segments (Details) link:presentationLink link:calculationLink link:definitionLink 100590 - Disclosure - Segment Information - Reconciliation of Information Reported by Segment to Condensed Consolidated Statement of Comprehensive Income Amounts (Details) link:presentationLink link:calculationLink link:definitionLink 100600 - Disclosure - Segment Information - Reconciliation of Information Reported by Segment to Condensed Consolidated Statement of Comprehensive Income Amounts (Parenthetical) (Details) link:presentationLink link:calculationLink link:definitionLink 100610 - Disclosure - Restructuring Costs - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100620 - Disclosure - Restructuring Costs - Summary of Total Restructuring Costs (Details) link:presentationLink link:calculationLink link:definitionLink 100630 - Disclosure - Restructuring Costs - Rollforward of Liability Associated with Cash-based Charges (Details) link:presentationLink link:calculationLink link:definitionLink 100640 - Disclosure - Income Taxes - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100650 - Disclosure - Goodwill and Other Intangible Assets - Components of Goodwill (Details) link:presentationLink link:calculationLink link:definitionLink 100660 - Disclosure - Goodwill and Other Intangible Assets - Changes in the Net Carrying Amount of the Components of Finite-Lived Intangible Assets (Details) link:presentationLink link:calculationLink link:definitionLink 100670 - Disclosure - Goodwill and Other Intangible Assets - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100680 - Disclosure - Goodwill and Other Intangible Assets - Schedule of Future Estimated Amortization Expense for Amortizable Intangible Assets (Details) link:presentationLink link:calculationLink link:definitionLink 100690 - Disclosure - Derivative Financial Instruments - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100700 - Disclosure - Derivative Financial Instruments - Schedule of Derivative Instruments Designated As Hedging Instrument Effect on Condensed Consolidated Statements of Comprehensive Income (Details) link:presentationLink link:calculationLink link:definitionLink 100710 - Disclosure - Derivative Financial Instruments - Schedule of Derivative Instruments, Effect on Condensed Consolidated Statements of Comprehensive Income (Details) link:presentationLink link:calculationLink link:definitionLink 100720 - Disclosure - Debt - Schedule of Current and Long-term Debt (Details) link:presentationLink link:calculationLink link:definitionLink 100730 - Disclosure - Debt - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100740 - Disclosure - Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) link:presentationLink link:calculationLink link:definitionLink 100750 - Disclosure - Fair Value Measurements - Fair Value Liabilities Measured Using Significant Unobservable Inputs Level 3 (Details) link:presentationLink link:calculationLink link:definitionLink 100760 - Disclosure - Fair Value Measurements - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100770 - Disclosure - Fair Value Measurements - Schedule of Liabilities Whose Carrying Values Differ From the Fair Value and are Not Measured on a Recurring Basis (Details) link:presentationLink link:calculationLink link:definitionLink 100780 - Disclosure - Retirement Benefits - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100790 - Disclosure - Retirement Benefits - Net Periodic Benefit Cost (Details) link:presentationLink link:calculationLink link:definitionLink 100800 - Disclosure - Leases - Schedule of Lease Costs Recorded in Condensed Consolidated Statements of Comprehensive Income (Details) link:presentationLink link:calculationLink link:definitionLink 100810 - Disclosure - Leases - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100820 - Disclosure - Commitments and Contingencies - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100830 - Disclosure - Supplementary Information for Certain Balance Sheet Accounts - Prepaid and Other Current Assets (Details) link:presentationLink link:calculationLink link:definitionLink 100840 - Disclosure - Supplementary Information for Certain Balance Sheet Accounts - Deferred Revenue and Accrued Expenses (Details) link:presentationLink link:calculationLink link:definitionLink 100850 - Disclosure - Supplementary Information for Certain Balance Sheet Accounts - Other Current Liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 100860 - Disclosure - Supplementary Information for Certain Balance Sheet Accounts - Provision For Liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 100870 - Disclosure - Supplementary Information for Certain Balance Sheet Accounts - Other Non-Current Liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 100880 - Disclosure - Other Income, Net (Details) link:presentationLink link:calculationLink link:definitionLink 100890 - Disclosure - Other Income, Net (Parenthetical ) (Details) link:presentationLink link:calculationLink link:definitionLink 100900 - Disclosure - Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) link:presentationLink link:calculationLink link:definitionLink 100910 - Disclosure - Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Details) link:presentationLink link:calculationLink link:definitionLink 100920 - Disclosure - Earnings Per Share - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 100930 - Disclosure - Earnings Per Share - Basic and Diluted Earnings Per Share (Details) link:presentationLink link:calculationLink link:definitionLink 100940 - Disclosure - Supplemental Disclosures of Cash Flow Information (Details) link:presentationLink link:calculationLink link:definitionLink 100950 - Disclosure - Supplemental Disclosures of Cash Flow Information - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink