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Business Combinations - Summary of Estimated Fair Values of Net Assets Acquired (Detail) $ in Millions | 3 Months Ended
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Mar. 31, 2026 USD ($) acquisition | Mar. 31, 2025 acquisition
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |
Cash and cash equivalents | $ 11 |
Fiduciary assets | 11 |
Other current assets | 1 |
Fixed assets | 3 |
Noncurrent assets | 1 |
Goodwill | 201 |
Expiration lists | 162 |
Non-compete agreements | 13 |
Total assets acquired | 403 |
Fiduciary liabilities | 11 |
Current liabilities | 11 |
Noncurrent liabilities | 47 |
Total liabilities assumed | 69 |
Total net assets acquired | $ 334 |
Number of companies acquired | acquisition | 51 | 28
Krose GmbH & Co KG February 25, 2026 (KGC) |  |
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |
Cash and cash equivalents | $ 4 |
Fiduciary assets | 6 |
Other current assets | 1 |
Fixed assets | 3 |
Noncurrent assets | 0 |
Goodwill | 145 |
Expiration lists | 102 |
Non-compete agreements | 11 |
Total assets acquired | 272 |
Fiduciary liabilities | 6 |
Current liabilities | 10 |
Noncurrent liabilities | 36 |
Total liabilities assumed | 52 |
Total net assets acquired | 220 |
Eight other acquisitions completed in 2026 |  |
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |
Cash and cash equivalents | 7 |
Fiduciary assets | 5 |
Other current assets | 0 |
Fixed assets | 0 |
Noncurrent assets | 1 |
Goodwill | 56 |
Expiration lists | 60 |
Non-compete agreements | 2 |
Total assets acquired | 131 |
Fiduciary liabilities | 5 |
Current liabilities | 1 |
Noncurrent liabilities | 11 |
Total liabilities assumed | 17 |
Total net assets acquired | $ 114 |
Number of companies acquired | acquisition | 8 |

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