v3.26.3
Segment Information - Schedule of Segment Reporting Information by Segment (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Jun. 30, 2026
Mar. 31, 2026
Sep. 30, 2025
Jun. 30, 2025
Mar. 31, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]                  
Revenues before reimbursements $ 3,930.0     $ 3,325.0     $ 12,601.0 $ 10,192.0  
Reimbursements 46.0     40.0     136.0 122.0  
Total revenues 3,976.0     3,365.0     12,737.0 10,314.0  
Compensation 2,237.0     1,932.0     7,083.0 5,633.0  
Operating 645.0     581.0     1,967.0 1,590.0  
Reimbursements 46.0     40.0     136.0 122.0  
Interest 168.0     161.0     494.0 477.0  
Depreciation 58.0     54.0     176.0 149.0  
Amortization 291.0     222.0     870.0 612.0  
Change in estimated acquisition earnout payables 16.0     29.0     39.0 39.0  
Total expenses 3,461.0     3,019.0     10,765.0 8,622.0  
Earnings before income taxes 515.0     346.0     1,972.0 1,692.0  
Provision (benefit) for income taxes 109.0     73.0     419.0 342.0  
Net earnings 406.0 $ 324.0 $ 823.0 273.0 $ 368.0 $ 709.0 1,553.0 1,350.0  
Net earnings attributable to noncontrolling interests 3.0     1.0     4.0 6.0  
Net earnings attributable to controlling interests 403.0     272.0     1,549.0 1,344.0  
Net foreign exchange loss 12.0     (2.0)     10.0 49.0  
Assets 79,064.0     79,068.0     79,064.0 79,068.0 $ 70,665.0
Goodwill 23,385.0     22,213.0     23,385.0 22,213.0 22,593.0
Amortizable intangible assets - net 10,202.0     10,754.0     10,202.0 10,754.0  
United States                  
Segment Reporting [Line Items]                  
Total revenues 2,812.0     2,371.0     8,827.0 6,882.0  
Assets 44,752.0     44,696.0     44,752.0 44,696.0  
Goodwill 15,926.0           15,926.0   16,537.0
United Kingdom                  
Segment Reporting [Line Items]                  
Total revenues 560.0     512.0     2,051.0 1,880.0  
Assets 19,197.0     21,486.0     19,197.0 21,486.0  
Goodwill 3,662.0           3,662.0   3,031.0
Australia                  
Segment Reporting [Line Items]                  
Total revenues 177.0     151.0     505.0 432.0  
Assets 2,597.0     2,327.0     2,597.0 2,327.0  
Goodwill 895.0           895.0   829.0
Canada                  
Segment Reporting [Line Items]                  
Total revenues 106.0     90.0     304.0 298.0  
Assets 2,250.0     1,733.0     2,250.0 1,733.0  
Goodwill 883.0           883.0   628.0
New Zealand                  
Segment Reporting [Line Items]                  
Total revenues 55.0     54.0     157.0 152.0  
Assets 752.0     777.0     752.0 777.0  
Goodwill 231.0           231.0   233.0
Other foreign                  
Segment Reporting [Line Items]                  
Total revenues 266.0     187.0     893.0 670.0  
Assets 9,516.0     8,049.0     9,516.0 8,049.0  
Goodwill 1,788.0           1,788.0   1,335.0
Commissions                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 2,371.0     1,908.0     7,936.0 5,965.0  
Fees                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 1,224.0     1,058.0     3,619.0 3,005.0  
Supplemental revenues                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 148.0     117.0     469.0 334.0  
Contingent revenues                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 74.0     75.0     280.0 241.0  
Interest income, premium finance revenues and other income                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 113.0     167.0     297.0 647.0  
Brokerage                  
Segment Reporting [Line Items]                  
Goodwill 22,839.0           22,839.0   22,078.0
Brokerage | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 3,473.0     2,922.0     11,268.0 9,023.0  
Reimbursements 0.0     0.0     0.0 0.0  
Total revenues 3,473.0     2,922.0     11,268.0 9,023.0  
Compensation 1,929.0     1,649.0     6,157.0 4,792.0  
Operating 508.0     434.0     1,565.0 1,149.0  
Reimbursements 0.0     0.0     0.0 0.0  
Interest 0.0     0.0     0.0 0.0  
Depreciation 46.0     42.0     140.0 113.0  
Amortization 284.0     218.0     849.0 596.0  
Change in estimated acquisition earnout payables 15.0     29.0     36.0 38.0  
Total expenses 2,782.0     2,372.0     8,747.0 6,688.0  
Earnings before income taxes 691.0     550.0     2,521.0 2,335.0  
Provision (benefit) for income taxes 176.0     141.0     643.0 600.0  
Net earnings 515.0     409.0     1,878.0 1,735.0  
Net earnings attributable to noncontrolling interests 3.0     1.0     4.0 6.0  
Net earnings attributable to controlling interests 512.0     408.0     1,874.0 1,729.0  
Net foreign exchange loss 3.0     2.0     6.0 3.0  
Assets 74,499.0     60,090.0     74,499.0 60,090.0  
Goodwill 22,839.0     21,739.0     22,839.0 21,739.0 22,078.0
Amortizable intangible assets - net 9,994.0     10,581.0     9,994.0 10,581.0  
Brokerage | Operating Segments | United States                  
Segment Reporting [Line Items]                  
Total revenues 2,422.0     2,021.0     7,682.0 5,856.0  
Assets 41,351.0     26,735.0     41,351.0 26,735.0  
Goodwill 15,817.0           15,817.0   16,428.0
Brokerage | Operating Segments | United Kingdom                  
Segment Reporting [Line Items]                  
Total revenues 529.0     485.0     1,960.0 1,803.0  
Assets 18,747.0     21,066.0     18,747.0 21,066.0  
Goodwill 3,514.0           3,514.0   2,889.0
Brokerage | Operating Segments | Australia                  
Segment Reporting [Line Items]                  
Total revenues 102.0     89.0     292.0 255.0  
Assets 2,104.0     1,887.0     2,104.0 1,887.0  
Goodwill 643.0           643.0   591.0
Brokerage | Operating Segments | Canada                  
Segment Reporting [Line Items]                  
Total revenues 104.0     88.0     297.0 292.0  
Assets 2,241.0     1,726.0     2,241.0 1,726.0  
Goodwill 883.0           883.0   628.0
Brokerage | Operating Segments | New Zealand                  
Segment Reporting [Line Items]                  
Total revenues 55.0     54.0     157.0 152.0  
Assets 745.0     768.0     745.0 768.0  
Goodwill 223.0           223.0   225.0
Brokerage | Operating Segments | Other foreign                  
Segment Reporting [Line Items]                  
Total revenues 261.0     185.0     880.0 665.0  
Assets 9,311.0     7,908.0     9,311.0 7,908.0  
Goodwill 1,759.0           1,759.0   1,317.0
Brokerage | Commissions | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 2,371.0     1,908.0     7,936.0 5,965.0  
Brokerage | Fees | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 776.0     665.0     2,306.0 1,864.0  
Brokerage | Supplemental revenues | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 148.0     117.0     469.0 334.0  
Brokerage | Contingent revenues | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 74.0     75.0     280.0 241.0  
Brokerage | Interest income, premium finance revenues and other income | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 104.0     157.0     277.0 619.0  
Risk Management                  
Segment Reporting [Line Items]                  
Goodwill 530.0           530.0   497.0
Risk Management | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 457.0     402.0     1,338.0 1,168.0  
Reimbursements 46.0     40.0     136.0 122.0  
Total revenues 503.0     442.0     1,474.0 1,290.0  
Compensation 271.0     244.0     809.0 719.0  
Operating 85.0     76.0     246.0 220.0  
Reimbursements 46.0     40.0     136.0 122.0  
Interest 0.0     0.0     0.0 0.0  
Depreciation 10.0     10.0     30.0 30.0  
Amortization 7.0     4.0     21.0 16.0  
Change in estimated acquisition earnout payables 1.0     0.0     3.0 1.0  
Total expenses 420.0     374.0     1,245.0 1,108.0  
Earnings before income taxes 83.0     68.0     229.0 182.0  
Provision (benefit) for income taxes 22.0     18.0     61.0 48.0  
Net earnings 61.0     50.0     168.0 134.0  
Net earnings attributable to noncontrolling interests 0.0     0.0     0.0 0.0  
Net earnings attributable to controlling interests 61.0     50.0     168.0 134.0  
Net foreign exchange loss 0.0     0.0     0.0 1.0  
Assets 2,421.0     2,047.0     2,421.0 2,047.0  
Goodwill 530.0     456.0     530.0 456.0 497.0
Amortizable intangible assets - net 208.0     173.0     208.0 173.0  
Risk Management | Operating Segments | United States                  
Segment Reporting [Line Items]                  
Total revenues 390.0     349.0     1,150.0 1,025.0  
Assets 1,420.0     1,154.0     1,420.0 1,154.0  
Goodwill 109.0           109.0   109.0
Risk Management | Operating Segments | United Kingdom                  
Segment Reporting [Line Items]                  
Total revenues 31.0     27.0     91.0 77.0  
Assets 450.0     419.0     450.0 419.0  
Goodwill 148.0           148.0   142.0
Risk Management | Operating Segments | Australia                  
Segment Reporting [Line Items]                  
Total revenues 75.0     62.0     213.0 177.0  
Assets 493.0     440.0     493.0 440.0  
Goodwill 252.0           252.0   238.0
Risk Management | Operating Segments | Canada                  
Segment Reporting [Line Items]                  
Total revenues 2.0     2.0     7.0 6.0  
Assets 9.0     7.0     9.0 7.0  
Goodwill 0.0           0.0   0.0
Risk Management | Operating Segments | New Zealand                  
Segment Reporting [Line Items]                  
Total revenues 0.0     0.0     0.0 0.0  
Assets 7.0     9.0     7.0 9.0  
Goodwill 8.0           8.0   8.0
Risk Management | Operating Segments | Other foreign                  
Segment Reporting [Line Items]                  
Total revenues 5.0     2.0     13.0 5.0  
Assets 42.0     18.0     42.0 18.0  
Goodwill 13.0           13.0   0.0
Risk Management | Commissions | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     0.0     0.0 0.0  
Risk Management | Fees | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 448.0     393.0     1,313.0 1,141.0  
Risk Management | Supplemental revenues | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     0.0     0.0 0.0  
Risk Management | Contingent revenues | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     0.0     0.0 0.0  
Risk Management | Interest income, premium finance revenues and other income | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 9.0     9.0     25.0 27.0  
Corporate                  
Segment Reporting [Line Items]                  
Goodwill 16.0           16.0   18.0
Corporate | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     1.0     (5.0) 1.0  
Reimbursements 0.0     0.0     0.0 0.0  
Total revenues 0.0     1.0     (5.0) 1.0  
Compensation 37.0     39.0     117.0 122.0  
Operating 52.0     71.0     156.0 221.0  
Reimbursements 0.0     0.0     0.0 0.0  
Interest 168.0     161.0     494.0 477.0  
Depreciation 2.0     2.0     6.0 6.0  
Amortization 0.0     0.0     0.0 0.0  
Change in estimated acquisition earnout payables 0.0     0.0     0.0 0.0  
Total expenses 259.0     273.0     773.0 826.0  
Earnings before income taxes (259.0)     (272.0)     (778.0) (825.0)  
Provision (benefit) for income taxes (89.0)     (86.0)     (285.0) (306.0)  
Net earnings (170.0)     (186.0)     (493.0) (519.0)  
Net earnings attributable to noncontrolling interests 0.0     0.0     0.0 0.0  
Net earnings attributable to controlling interests (170.0)     (186.0)     (493.0) (519.0)  
Net foreign exchange loss 9.0     (4.0)     4.0 45.0  
Assets 2,144.0     16,931.0     2,144.0 16,931.0  
Goodwill 16.0     18.0     16.0 18.0 18.0
Amortizable intangible assets - net 0.0     0.0     0.0 0.0  
Corporate | Operating Segments | United States                  
Segment Reporting [Line Items]                  
Total revenues 0.0     1.0     (5.0) 1.0  
Assets 1,981.0     16,807.0     1,981.0 16,807.0  
Goodwill 0.0           0.0   0.0
Corporate | Operating Segments | United Kingdom                  
Segment Reporting [Line Items]                  
Total revenues 0.0     0.0     0.0 0.0  
Assets 0.0     1.0     0.0 1.0  
Goodwill 0.0           0.0   0.0
Corporate | Operating Segments | Australia                  
Segment Reporting [Line Items]                  
Total revenues 0.0     0.0     0.0 0.0  
Assets 0.0     0.0     0.0 0.0  
Goodwill 0.0           0.0   0.0
Corporate | Operating Segments | Canada                  
Segment Reporting [Line Items]                  
Total revenues 0.0     0.0     0.0 0.0  
Assets 0.0     0.0     0.0 0.0  
Goodwill 0.0           0.0   0.0
Corporate | Operating Segments | New Zealand                  
Segment Reporting [Line Items]                  
Total revenues 0.0     0.0     0.0 0.0  
Assets 0.0     0.0     0.0 0.0  
Goodwill 0.0           0.0   0.0
Corporate | Operating Segments | Other foreign                  
Segment Reporting [Line Items]                  
Total revenues 0.0     0.0     0.0 0.0  
Assets 163.0     123.0     163.0 123.0  
Goodwill 16.0           16.0   $ 18.0
Corporate | Commissions | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     0.0     0.0 0.0  
Corporate | Fees | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     0.0     0.0 0.0  
Corporate | Supplemental revenues | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     0.0     0.0 0.0  
Corporate | Contingent revenues | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements 0.0     0.0     0.0 0.0  
Corporate | Interest income, premium finance revenues and other income | Operating Segments                  
Segment Reporting [Line Items]                  
Revenues before reimbursements $ 0.0     $ 1.0     $ (5.0) $ 1.0