v3.26.3
Fair Value Measurements and Investments - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)
$ in Millions
Sep. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Contingent consideration [Member] | Fair Value Inputs, Discount Rate [Member]    
Liabilities:    
Fair value inputs, weighted-average discount rate 0.1131 0.11
Contingent consideration [Member] | Fair Value Inputs, Discount Rate [Member] | Minimum [Member]    
Liabilities:    
Fair value inputs, weighted-average discount rate 0.11  
Contingent consideration [Member] | Fair Value Inputs, Discount Rate [Member] | Maximum [Member]    
Liabilities:    
Fair value inputs, weighted-average discount rate 0.134  
Recurring [Member]    
Assets:    
Mutual funds / exchange traded funds [1] $ 152 $ 145
Derivative financial instruments [2] 2 5
Liabilities:    
Contingent consideration [3] 73 14
Derivative financial instruments 4 [4] 1 [2]
Recurring [Member] | Location, Statement of Financial Position, Balance [Axis]: us-gaap:FundsHeldForClients    
Assets:    
Mutual funds / exchange traded funds 539 448
Recurring [Member] | Commingled Funds [Member]    
Assets:    
Deferred compensation plans [1],[5] 31 31
Recurring [Member] | Hedge Funds [Member]    
Assets:    
Deferred compensation plans [1],[6] 28 28
Recurring [Member] | Debt securities    
Assets:    
Mutual funds / exchange traded funds 51  
Recurring [Member] | Level 1 [Member]    
Assets:    
Mutual funds / exchange traded funds [1] 152 145
Derivative financial instruments [2] 0 0
Liabilities:    
Contingent consideration [3] 0 0
Derivative financial instruments 0 [4] 0 [2]
Recurring [Member] | Level 1 [Member] | Location, Statement of Financial Position, Balance [Axis]: us-gaap:FundsHeldForClients    
Assets:    
Mutual funds / exchange traded funds 539 448
Recurring [Member] | Level 1 [Member] | Commingled Funds [Member]    
Assets:    
Deferred compensation plans [1],[5] 0 0
Recurring [Member] | Level 1 [Member] | Hedge Funds [Member]    
Assets:    
Deferred compensation plans [1],[6] 0 0
Recurring [Member] | Level 1 [Member] | Debt securities    
Assets:    
Mutual funds / exchange traded funds 51  
Recurring [Member] | Level 2 [Member]    
Assets:    
Mutual funds / exchange traded funds [1] 0 0
Derivative financial instruments [2] 2 5
Liabilities:    
Contingent consideration [3] 0 0
Derivative financial instruments 4 [4] 1 [2]
Recurring [Member] | Level 2 [Member] | Location, Statement of Financial Position, Balance [Axis]: us-gaap:FundsHeldForClients    
Assets:    
Mutual funds / exchange traded funds 0 0
Recurring [Member] | Level 2 [Member] | Commingled Funds [Member]    
Assets:    
Deferred compensation plans [1],[5] 0 0
Recurring [Member] | Level 2 [Member] | Hedge Funds [Member]    
Assets:    
Deferred compensation plans [1],[6] 0 0
Recurring [Member] | Level 2 [Member] | Debt securities    
Assets:    
Mutual funds / exchange traded funds 0  
Recurring [Member] | Level 3 [Member]    
Assets:    
Mutual funds / exchange traded funds [1] 0 0
Derivative financial instruments [2] 0 0
Liabilities:    
Contingent consideration [3] 73 14
Derivative financial instruments 0 [4] 0 [2]
Recurring [Member] | Level 3 [Member] | Location, Statement of Financial Position, Balance [Axis]: us-gaap:FundsHeldForClients    
Assets:    
Mutual funds / exchange traded funds 0 0
Recurring [Member] | Level 3 [Member] | Commingled Funds [Member]    
Assets:    
Deferred compensation plans [1],[5] 0 0
Recurring [Member] | Level 3 [Member] | Hedge Funds [Member]    
Assets:    
Deferred compensation plans [1],[6] 0 $ 0
Recurring [Member] | Level 3 [Member] | Debt securities    
Assets:    
Mutual funds / exchange traded funds $ 0  
[1] With the exception of the funds included in fiduciary assets, the majority of these balances are held as part of deferred compensation plans with related liabilities in other current liabilities and other non-current liabilities on the condensed consolidated balance sheets.
[2] See Note 9 — Derivative Financial Instruments for further information on our derivative contracts.
[3] At September 30, 2026 and December 31, 2025, represents consideration due to be paid across multiple years until 2031 and 2029, respectively. Probability weightings are based on our knowledge of the past and planned performance of the acquired entity to which the contingent consideration applies. The fair value weighted-average discount rates used in our material contingent consideration calculations were 11.31% and 11.00% at September 30, 2026 and December 31, 2025, respectively. The range of these discount rates was 11.00% - 13.40% at September 30, 2026. Using different probability weightings and discount rates could result in an increase or decrease of the contingent consideration payable.
[4] Realized and unrealized gains include accretion and adjustments to contingent consideration liabilities, which are included within Interest expense and Other operating expenses, respectively, on the condensed consolidated statements of comprehensive income.
[5] Consists of the Towers Watson Global Equity Focus Fund, for which redemptions can occur on any business day, and require a minimum of one business day’s notice.
[6] Consists of the Towers Watson Alternative Credit Fund, for which the redemption period is generally quarterly, however requires a 50-day notice.