v3.25.4
Goodwill and Intangible Assets - Changes in Goodwill and Intangible Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Changes in goodwill and intangible assets    
Goodwill and intangible assets, beginning balance $ 8,278.2 $ 6,376.3
Additions 585.0 2,538.7
Disposals (339.0) (44.1)
Amortization (265.1) (266.5)
Impairments (101.4) (95.5)
Foreign exchange effect and other 181.7 (230.7)
Goodwill and intangible assets, ending balance 8,339.4 8,278.2
Aggregate carrying value of Intangible assets with indefinite useful life 2,345.7 2,294.7
Aggregate carrying value of intangible assets with a finite useful life 1,763.3 $ 1,858.6
Boat Rocker    
Changes in goodwill and intangible assets    
Impairment of intangible assets $ 108.6  
Customer and broker relationships | Minimum    
Changes in goodwill and intangible assets    
Intangible assets with a finite useful life 8 years 8 years
Customer and broker relationships | Maximum    
Changes in goodwill and intangible assets    
Intangible assets with a finite useful life 20 years 20 years
Computer software | Minimum    
Changes in goodwill and intangible assets    
Intangible assets with a finite useful life 3 years 3 years
Computer software | Maximum    
Changes in goodwill and intangible assets    
Intangible assets with a finite useful life 15 years 15 years
Brand names    
Changes in goodwill and intangible assets    
Aggregate carrying value of Intangible assets with indefinite useful life $ 1,753.2 $ 1,700.5
Goodwill    
Changes in goodwill and intangible assets    
Goodwill and intangible assets, beginning balance 4,124.9 3,121.9
Additions 140.1 1,152.5
Disposals (76.8) (22.9)
Impairments (32.0) (30.3)
Foreign exchange effect and other 74.2 (96.3)
Goodwill and intangible assets, ending balance 4,230.4 4,124.9
Lloyd's participation rights    
Changes in goodwill and intangible assets    
Goodwill and intangible assets, beginning balance 503.2 503.2
Goodwill and intangible assets, ending balance 503.2 503.2
Customer and broker relationships    
Changes in goodwill and intangible assets    
Goodwill and intangible assets, beginning balance 1,203.5 1,070.6
Additions 3.8 335.8
Disposals   (17.0)
Amortization (132.9) (125.0)
Impairments (2.1) (52.0)
Foreign exchange effect and other 21.4 (8.9)
Goodwill and intangible assets, ending balance 1,093.7 1,203.5
Brand names    
Changes in goodwill and intangible assets    
Goodwill and intangible assets, beginning balance 1,844.6 1,169.9
Additions 268.7 777.9
Disposals (236.4) (1.0)
Amortization (10.4) (2.8)
Impairments   (2.6)
Foreign exchange effect and other 65.0 (96.8)
Goodwill and intangible assets, ending balance 1,931.5 1,844.6
Computer software and other    
Changes in goodwill and intangible assets    
Goodwill and intangible assets, beginning balance 602.0 510.7
Additions 172.4 272.5
Disposals (25.8) (3.2)
Amortization (121.8) (138.7)
Impairments (67.3) (10.6)
Foreign exchange effect and other 21.1 (28.7)
Goodwill and intangible assets, ending balance 580.6 602.0
Intangible assets other than goodwill    
Changes in goodwill and intangible assets    
Goodwill and intangible assets, beginning balance 4,153.3 3,254.4
Additions 444.9 1,386.2
Disposals (262.2) (21.2)
Amortization (265.1) (266.5)
Impairments (69.4) (65.2)
Foreign exchange effect and other 107.5 (134.4)
Goodwill and intangible assets, ending balance $ 4,109.0 $ 4,153.3