v3.26.1
Acquisitions and Dispositions (Narrative) (Details)
$ in Millions
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2026
USD ($)
Jun. 30, 2026
USD ($)
Jun. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
Jun. 30, 2026
USD ($)
acquisition
Jun. 30, 2025
USD ($)
Dec. 31, 2025
insuranceBroker
acquisition
Jul. 21, 2026
Jan. 31, 2025
Business Combination [Line Items]                  
Total consideration         $ 181 $ 148      
Cash paid         132 86      
Estimated fair value of deferred/contingent consideration         49 47      
Deferred purchase consideration from prior years' acquisitions         19 36      
Acquisition related costs   $ 55 $ 58   103 137      
Number of insurance brokers acquired | insuranceBroker             3    
Fair value of previously-held equity method investment           15      
Payment to acquire non-controlling interest $ 54       54 0      
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Marsh Management Consulting Celent Advisory Business                  
Business Combination [Line Items]                  
Cash proceeds from sale       $ 25          
Net gain included in revenue consolidated statements of income       15          
Prior Fiscal Periods Acquisitions                  
Business Combination [Line Items]                  
Estimated fair value of deferred/contingent consideration         96        
Deferred purchase consideration from prior years' acquisitions           36      
Contingent consideration from prior year's acquisitions           26      
Mc Griff Insurance Services L L C                  
Business Combination [Line Items]                  
Acquisition related costs   $ 47 $ 45   $ 89 $ 114      
Carpenter Turner Cyprus Ltd.                  
Business Combination [Line Items]                  
Ownership share (as a percent)                 51.50%
Gain on previously-held equity method investment, fair value       $ 13          
Deasterra Partners, S.L. | Subsequent Event                  
Business Combination [Line Items]                  
Ownership share (as a percent)               60.00%  
Minimum                  
Business Combination [Line Items]                  
Revenue target period (in years)         2 years 2 years      
Maximum                  
Business Combination [Line Items]                  
Revenue target period (in years)         4 years 4 years      
Risk and Insurance Services                  
Business Combination [Line Items]                  
Number of acquisitions made (in acquisitions) | acquisition         3   14    
Consulting                  
Business Combination [Line Items]                  
Number of acquisitions made (in acquisitions) | acquisition         2   6