XML 56 R49.htm IDEA: XBRL DOCUMENT v3.24.3
Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2024
Dec. 31, 2023
Goodwill [Line Items]    
Beginning Balance $ 11,475.6  
Goodwill acquired during the period 410.7  
Goodwill true-ups due to appraisals and other acquisition adjustments (see Note 3) 188.9 $ 256.7
Goodwill written-off related to sales of business and impairment (5.8)  
Foreign currency translation adjustments during the period 124.0  
Ending Balance 12,193.4 11,475.6
Brokerage [Member]    
Goodwill [Line Items]    
Beginning Balance 11,217.8  
Goodwill acquired during the period 410.7  
Goodwill true-ups due to appraisals and other acquisition adjustments (see Note 3) 87.4  
Goodwill written-off related to sales of business and impairment (5.8)  
Foreign currency translation adjustments during the period 119.2  
Ending Balance 11,829.3 11,217.8
Risk Management [Member]    
Goodwill [Line Items]    
Beginning Balance 238.8  
Goodwill true-ups due to appraisals and other acquisition adjustments (see Note 3) 101.5  
Foreign currency translation adjustments during the period 4.9  
Ending Balance 345.2 238.8
Corporate [Member]    
Goodwill [Line Items]    
Beginning Balance 19.0  
Foreign currency translation adjustments during the period (0.1)  
Ending Balance $ 18.9 $ 19.0