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v3.22.2.2

Segment Information - Summary of Geographical Location and Segment (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | $ 2,044.0 | $ 2,138.2 | $ 6,522.3 | $ 6,236.7
Unites States [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 1,401.0 | 1,592.1 | 4,268.3 | 4,513.8
United Kingdom [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 326.6 | 288.6 | 1,216.5 | 930.0
Australia [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 103.0 | 92.0 | 304.6 | 278.7
Canada [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 82.3 | 69.7 | 266.4 | 219.9
New Zealand [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 44.6 | 44.4 | 133.3 | 130.0
Other Foreign [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 86.5 | 51.4 | 333.2 | 164.3
Brokerage [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 1,736.2 | 1,499.7 | 5,599.5 | 4,500.1
Brokerage [Member] | Unites States [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 1,140.3 | 1,000.3 | 3,492.0 | 2,919.3
Brokerage [Member] | United Kingdom [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 315.7 | 276.5 | 1,182.1 | 895.0
Brokerage [Member] | Australia [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 71.8 | 62.4 | 207.4 | 187.1
Brokerage [Member] | Canada [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 80.6 | 68.1 | 261.9 | 215.5
Brokerage [Member] | New Zealand [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 41.3 | 41.0 | 122.9 | 118.9
Brokerage [Member] | Other Foreign [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 86.5 | 51.4 | 333.2 | 164.3
Risk Management [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 307.5 | 280.6 | 899.4 | 815.0
Risk Management [Member] | Unites States [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 260.4 | 233.9 | 752.9 | 672.9
Risk Management [Member] | United Kingdom [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 10.9 | 12.1 | 34.4 | 35.0
Risk Management [Member] | Australia [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 31.2 | 29.6 | 97.2 | 91.6
Risk Management [Member] | Canada [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 1.7 | 1.6 | 4.5 | 4.4
Risk Management [Member] | New Zealand [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 3.3 | 3.4 | 10.4 | 11.1
Corporate [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | 0.3 | 357.9 | 23.4 | 921.6
Corporate [Member] | Unites States [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total revenues | $ 0.3 | $ 357.9 | $ 23.4 | $ 921.6

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