v3.26.3
Business Combinations - Acquisition Method for Recording Business Combinations (Detail)
shares in Thousands, $ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
acquisition
Sep. 30, 2025
acquisition
Sep. 30, 2026
USD ($)
acquisition
shares
Sep. 30, 2025
acquisition
Business Combination [Line Items]        
Number of companies acquired | acquisition 30 41 94 82
2026 Acquisitions        
Business Combination [Line Items]        
Common Shares Issued (in shares) | shares     66  
Common Shares Value     $ 15.0  
Cash Paid     1,073.0  
Accrued Liability $ 11.0   11.0  
Escrow Deposited 31.0   31.0  
Recorded Earnout Payable     117.0  
Total Recorded Purchase Price 1,247.0   1,247.0  
Maximum Potential Earnout Payable 262.0   $ 262.0  
Krose GmbH & Co KG February 25, 2026 (KGC)        
Business Combination [Line Items]        
Common Shares Issued (in shares) | shares     66  
Common Shares Value     $ 15.0  
Cash Paid     203.0  
Accrued Liability 2.0   2.0  
Escrow Deposited 0.0   0.0  
Recorded Earnout Payable     0.0  
Total Recorded Purchase Price 220.0   220.0  
Maximum Potential Earnout Payable 0.0   $ 0.0  
McKee Risk Management, Inc. May 1, 2026 (MRM)        
Business Combination [Line Items]        
Common Shares Issued (in shares) | shares     0  
Common Shares Value     $ 0.0  
Cash Paid     135.0  
Accrued Liability 0.0   0.0  
Escrow Deposited 5.0   5.0  
Recorded Earnout Payable     6.0  
Total Recorded Purchase Price 146.0   146.0  
Maximum Potential Earnout Payable 30.0   $ 30.0  
W.N. Tuscano Agency, Inc. July 1, 2026 (WNT)        
Business Combination [Line Items]        
Common Shares Issued (in shares) | shares     0  
Common Shares Value     $ 0.0  
Cash Paid     99.0  
Accrued Liability 0.0   0.0  
Escrow Deposited 3.0   3.0  
Recorded Earnout Payable     9.0  
Total Recorded Purchase Price 111.0   111.0  
Maximum Potential Earnout Payable 32.0   $ 32.0  
Wilson M. Beck Insurance Services, Inc. July 1, 2026 (WMB)        
Business Combination [Line Items]        
Common Shares Issued (in shares) | shares     0  
Common Shares Value     $ 0.0  
Cash Paid     292.0  
Accrued Liability 2.0   2.0  
Escrow Deposited 2.0   2.0  
Recorded Earnout Payable     17.0  
Total Recorded Purchase Price 313.0   313.0  
Maximum Potential Earnout Payable 61.0   $ 61.0  
Apollo Insurance Solutions Ltd. August 1, 2026 (APO)        
Business Combination [Line Items]        
Common Shares Issued (in shares) | shares     0  
Common Shares Value     $ 0.0  
Cash Paid     95.0  
Accrued Liability 1.0   1.0  
Escrow Deposited 6.0   6.0  
Recorded Earnout Payable     36.0  
Total Recorded Purchase Price 138.0   138.0  
Maximum Potential Earnout Payable 50.0   $ 50.0  
Sixteen other acquisitions completed in 2026        
Business Combination [Line Items]        
Common Shares Issued (in shares) | shares     0  
Common Shares Value     $ 0.0  
Cash Paid     249.0  
Accrued Liability 6.0   6.0  
Escrow Deposited 15.0   15.0  
Recorded Earnout Payable     49.0  
Total Recorded Purchase Price 319.0   319.0  
Maximum Potential Earnout Payable $ 89.0   $ 89.0  
Number of companies acquired | acquisition     16