v3.26.3
Business Combinations - Summary of Estimated Fair Values of Net Assets Acquired (Detail)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
acquisition
Sep. 30, 2025
acquisition
Sep. 30, 2026
USD ($)
acquisition
Sep. 30, 2025
acquisition
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]        
Cash and cash equivalents $ 53   $ 53  
Fiduciary assets 307   307  
Other current assets 46   46  
Fixed assets 8   8  
Noncurrent assets 14   14  
Goodwill 666   666  
Expiration lists 601   601  
Non-compete agreements 5   5  
Trade names 1   1  
Total assets acquired 1,701   1,701  
Fiduciary liabilities 307   307  
Current liabilities 34   34  
Noncurrent liabilities 113   113  
Total liabilities assumed 454   454  
Total net assets acquired $ 1,247   $ 1,247  
Number of companies acquired | acquisition 30 41 94 82
Krose GmbH & Co KG February 25, 2026 (KGC)        
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]        
Cash and cash equivalents $ 4   $ 4  
Fiduciary assets 6   6  
Other current assets 1   1  
Fixed assets 3   3  
Noncurrent assets 2   2  
Goodwill 102   102  
Expiration lists 120   120  
Non-compete agreements 1   1  
Trade names 0   0  
Total assets acquired 239   239  
Fiduciary liabilities 6   6  
Current liabilities 10   10  
Noncurrent liabilities 3   3  
Total liabilities assumed 19   19  
Total net assets acquired 220   220  
McKee Risk Management, Inc. May 1, 2026 (MRM)        
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]        
Cash and cash equivalents 4   4  
Fiduciary assets 32   32  
Other current assets 5   5  
Fixed assets 0   0  
Noncurrent assets 2   2  
Goodwill 64   64  
Expiration lists 77   77  
Non-compete agreements 0   0  
Trade names 0   0  
Total assets acquired 184   184  
Fiduciary liabilities 32   32  
Current liabilities 4   4  
Noncurrent liabilities 2   2  
Total liabilities assumed 38   38  
Total net assets acquired 146   146  
W.N. Tuscano Agency, Inc. July 1, 2026 (WNT)        
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]        
Cash and cash equivalents 10   10  
Fiduciary assets 18   18  
Other current assets 4   4  
Fixed assets 0   0  
Noncurrent assets 2   2  
Goodwill 50   50  
Expiration lists 53   53  
Non-compete agreements 0   0  
Trade names 0   0  
Total assets acquired 137   137  
Fiduciary liabilities 18   18  
Current liabilities 7   7  
Noncurrent liabilities 1   1  
Total liabilities assumed 26   26  
Total net assets acquired 111   111  
Wilson M. Beck Insurance Services, Inc. July 1, 2026 (WMB)        
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]        
Cash and cash equivalents 11   11  
Fiduciary assets 45   45  
Other current assets 9   9  
Fixed assets 5   5  
Noncurrent assets 4   4  
Goodwill 189   189  
Expiration lists 136   136  
Non-compete agreements 1   1  
Trade names 1   1  
Total assets acquired 401   401  
Fiduciary liabilities 45   45  
Current liabilities 4   4  
Noncurrent liabilities 39   39  
Total liabilities assumed 88   88  
Total net assets acquired 313   313  
Apollo Insurance Solutions Ltd. August 1, 2026 (APO)        
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]        
Cash and cash equivalents 19   19  
Fiduciary assets 6   6  
Other current assets 2   2  
Fixed assets 0   0  
Noncurrent assets 1   1  
Goodwill 81   81  
Expiration lists 57   57  
Non-compete agreements 0   0  
Trade names 0   0  
Total assets acquired 166   166  
Fiduciary liabilities 6   6  
Current liabilities 2   2  
Noncurrent liabilities 20   20  
Total liabilities assumed 28   28  
Total net assets acquired 138   138  
Sixteen other acquisitions completed in 2026        
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]        
Cash and cash equivalents 5   5  
Fiduciary assets 200   200  
Other current assets 25   25  
Fixed assets 0   0  
Noncurrent assets 3   3  
Goodwill 180   180  
Expiration lists 158   158  
Non-compete agreements 3   3  
Trade names 0   0  
Total assets acquired 574   574  
Fiduciary liabilities 200   200  
Current liabilities 7   7  
Noncurrent liabilities 48   48  
Total liabilities assumed 255   255  
Total net assets acquired $ 319   $ 319  
Number of companies acquired | acquisition     16