v3.8.0.1
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2017
Feb. 23, 2018
Jun. 30, 2017
Document and Entity Information [Abstract]      
Entity Registrant Name Willis Towers Watson Plc.    
Entity Central Index Key 0001140536    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag true    
Amendment Description This Amendment No. 1 on Form 10-K/A (the ‘Amendment’) amends Willis Towers Watson Public Limited Company’s (the ‘Company’) Annual Report on Form 10-K for the year ended December 31, 2017, as originally filed with the Securities and Exchange Commission on February 28, 2018 (the ‘Original Filing’). The Company is filing this Amendment solely to include an additional paragraph in the opinion on the 2017 financial statements of its independent auditor, Deloitte and Touche LLP, describing their procedures performed in auditing the 2017 adjustments of the Company’s reportable segment structure and adoption of ASU 2016-09 on a full retrospective basis to prior years, and their opinion on the appropriateness and proper application of such adjustments.    
Entity Common Stock, Shares Outstanding   132,216,177  
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 18,544,137,403