XML 80 R67.htm IDEA: XBRL DOCUMENT v3.22.0.1
Intangible Assets - Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations (Detail) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Goodwill [Line Items]      
Total goodwill - net $ 8,666.2 $ 6,127.0 $ 5,618.5
Unites States [Member]      
Goodwill [Line Items]      
Total goodwill - net 4,473.9 3,433.0  
United Kingdom [Member]      
Goodwill [Line Items]      
Total goodwill - net 2,213.7 1,343.4  
Canada [Member]      
Goodwill [Line Items]      
Total goodwill - net 572.9 492.9  
Australia [Member]      
Goodwill [Line Items]      
Total goodwill - net 498.1 473.6  
New Zealand [Member]      
Goodwill [Line Items]      
Total goodwill - net 227.8 232.6  
Other Foreign [Member]      
Goodwill [Line Items]      
Total goodwill - net 679.8 151.5  
Brokerage [Member]      
Goodwill [Line Items]      
Total goodwill - net 8,544.6 6,053.6 5,548.9
Brokerage [Member] | Unites States [Member]      
Goodwill [Line Items]      
Total goodwill - net 4,409.1 3,399.8  
Brokerage [Member] | United Kingdom [Member]      
Goodwill [Line Items]      
Total goodwill - net 2,198.7 1,328.3  
Brokerage [Member] | Canada [Member]      
Goodwill [Line Items]      
Total goodwill - net 572.9 492.9  
Brokerage [Member] | Australia [Member]      
Goodwill [Line Items]      
Total goodwill - net 487.2 462.1  
Brokerage [Member] | New Zealand [Member]      
Goodwill [Line Items]      
Total goodwill - net 217.6 221.9  
Brokerage [Member] | Other Foreign [Member]      
Goodwill [Line Items]      
Total goodwill - net 659.1 148.6  
Risk Management [Member]      
Goodwill [Line Items]      
Total goodwill - net 100.9 70.5 66.6
Risk Management [Member] | Unites States [Member]      
Goodwill [Line Items]      
Total goodwill - net 64.8 33.2  
Risk Management [Member] | United Kingdom [Member]      
Goodwill [Line Items]      
Total goodwill - net 15.0 15.1  
Risk Management [Member] | Australia [Member]      
Goodwill [Line Items]      
Total goodwill - net 10.9 11.5  
Risk Management [Member] | New Zealand [Member]      
Goodwill [Line Items]      
Total goodwill - net 10.2 10.7  
Corporate [Member]      
Goodwill [Line Items]      
Total goodwill - net 20.7 2.9 $ 3.0
Corporate [Member] | Other Foreign [Member]      
Goodwill [Line Items]      
Total goodwill - net $ 20.7 $ 2.9