v3.25.2
Acquisitions and Dispositions (Narrative) (Details)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jan. 01, 2024
USD ($)
Jun. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
Jun. 30, 2024
USD ($)
Mar. 31, 2024
USD ($)
Jun. 30, 2025
USD ($)
acquisition
Jun. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
acquisition
Jan. 31, 2025
Business Combination [Line Items]                  
Total consideration           $ 148 $ 716    
Cash paid           86 662    
Contingent purchase consideration           47 54    
Fair value of previously-held equity method investment           15      
Deferred purchase consideration from prior years' acquisitions           36 10    
Contingent consideration from prior year's acquisitions           7 71    
Acquisition related costs   $ 58   $ 21   $ 137 $ 29    
Marsh McLennan Agency's ("MMA") Technology Consulting And Administrative Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations                  
Business Combination [Line Items]                  
Cash proceeds from sale     $ 25            
Net gain included in revenue consolidated statements of income     15            
U.S. Health And Benefits And U.K Pension Administration Businesses | Disposal Group, Disposed of by Sale, Not Discontinued Operations                  
Business Combination [Line Items]                  
Cash proceeds from sale $ 114                
Exit costs         $ 18        
Certain Businesses Primarily in Brazil                  
Business Combination [Line Items]                  
Cash proceeds from sale               $ 21  
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    
Carpenter Turner Cyprus Ltd.                  
Business Combination [Line Items]                  
Ownership share (percent)                 51.50%
Gain on previously-held equity method investment, fair value     $ 13            
Prior Fiscal Periods Acquisitions                  
Business Combination [Line Items]                  
Deferred purchase consideration from prior years' acquisitions             $ 10    
Contingent consideration from prior year's acquisitions           $ 26 $ 161    
Mc Griff Insurance Services L L C                  
Business Combination [Line Items]                  
Acquisition related costs   $ 45       $ 114      
Risk and Insurance Services                  
Business Combination [Line Items]                  
Number of acquisitions made (in acquisitions) | acquisition           5   10  
Consulting                  
Business Combination [Line Items]                  
Number of acquisitions made (in acquisitions) | acquisition           2   7