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Business Combinations - Summary of Estimated Fair Values of Net Assets Acquired (Detail) $ in Millions | 3 Months Ended | 9 Months Ended | 285 Months Ended
--- | --- | --- | ---
Sep. 30, 2025 USD ($) acquisition | Sep. 30, 2024 acquisition | Sep. 30, 2025 USD ($) acquisition | Sep. 30, 2024 acquisition | Sep. 30, 2025 USD ($) company
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |  |  |  |
Cash and cash equivalents | $ 264.3 |  | $ 264.3 |  | $ 264.3
Fiduciary assets | 1,718.7 |  | 1,718.7 |  | 1,718.7
Other current assets | 1,148.9 |  | 1,148.9 |  | 1,148.9
Fixed assets | 151.6 |  | 151.6 |  | 151.6
Noncurrent assets | 264.9 |  | 264.9 |  | 264.9
Goodwill | 9,539.9 |  | 9,539.9 |  | 9,539.9
Expiration lists | 6,774.6 |  | 6,774.6 |  | 6,774.6
Non-compete agreements | 11.9 |  | 11.9 |  | 11.9
Trade names | 37.5 |  | 37.5 |  | 37.5
Total assets acquired | 19,912.3 |  | 19,912.3 |  | 19,912.3
Fiduciary liabilities | 1,718.7 |  | 1,718.7 |  | 1,718.7
Current liabilities | 937.1 |  | 937.1 |  | 937.1
Noncurrent liabilities | 1,448.1 |  | 1,448.1 |  | 1,448.1
Total liabilities assumed | 4,103.9 |  | 4,103.9 |  | 4,103.9
Total net assets acquired | $ 15,808.4 |  | $ 15,808.4 |  | $ 15,808.4
Number of companies acquired | 41 | 29 | 82 | 74 | 776
W K Webster & Co Ltd February 1, 2025 (WKW) |  |  |  |  |
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |  |  |  |
Cash and cash equivalents | $ 5.3 |  | $ 5.3 |  | $ 5.3
Fiduciary assets | 86.8 |  | 86.8 |  | 86.8
Other current assets | 16.7 |  | 16.7 |  | 16.7
Fixed assets | 2.8 |  | 2.8 |  | 2.8
Noncurrent assets | 2.2 |  | 2.2 |  | 2.2
Goodwill | 99.6 |  | 99.6 |  | 99.6
Expiration lists | 53.6 |  | 53.6 |  | 53.6
Non-compete agreements | 0.0 |  | 0.0 |  | 0.0
Trade names | 2.2 |  | 2.2 |  | 2.2
Total assets acquired | 269.2 |  | 269.2 |  | 269.2
Fiduciary liabilities | 86.8 |  | 86.8 |  | 86.8
Current liabilities | 11.8 |  | 11.8 |  | 11.8
Noncurrent liabilities | 16.0 |  | 16.0 |  | 16.0
Total liabilities assumed | 114.6 |  | 114.6 |  | 114.6
Total net assets acquired | 154.6 |  | 154.6 |  | 154.6
Case Group February 26, 2025 (CSG) |  |  |  |  |
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |  |  |  |
Cash and cash equivalents | 5.6 |  | 5.6 |  | 5.6
Fiduciary assets | 0.0 |  | 0.0 |  | 0.0
Other current assets | 4.0 |  | 4.0 |  | 4.0
Fixed assets | 1.0 |  | 1.0 |  | 1.0
Noncurrent assets | 0.3 |  | 0.3 |  | 0.3
Goodwill | 49.5 |  | 49.5 |  | 49.5
Expiration lists | 36.2 |  | 36.2 |  | 36.2
Non-compete agreements | 7.3 |  | 7.3 |  | 7.3
Trade names | 0.0 |  | 0.0 |  | 0.0
Total assets acquired | 103.9 |  | 103.9 |  | 103.9
Fiduciary liabilities | 0.0 |  | 0.0 |  | 0.0
Current liabilities | 7.3 |  | 7.3 |  | 7.3
Noncurrent liabilities | 13.8 |  | 13.8 |  | 13.8
Total liabilities assumed | 21.1 |  | 21.1 |  | 21.1
Total net assets acquired | 82.8 |  | 82.8 |  | 82.8
Woodruff Sawyer & Co April 10, 2025 (WSC) |  |  |  |  |
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |  |  |  |
Cash and cash equivalents | 61.9 |  | 61.9 |  | 61.9
Fiduciary assets | 465.3 |  | 465.3 |  | 465.3
Other current assets | 77.9 |  | 77.9 |  | 77.9
Fixed assets | 12.8 |  | 12.8 |  | 12.8
Noncurrent assets | 25.1 |  | 25.1 |  | 25.1
Goodwill | 811.9 |  | 811.9 |  | 811.9
Expiration lists | 459.2 |  | 459.2 |  | 459.2
Non-compete agreements | 0.0 |  | 0.0 |  | 0.0
Trade names | 8.4 |  | 8.4 |  | 8.4
Total assets acquired | 1,922.5 |  | 1,922.5 |  | 1,922.5
Fiduciary liabilities | 465.3 |  | 465.3 |  | 465.3
Current liabilities | 35.2 |  | 35.2 |  | 35.2
Noncurrent liabilities | 147.7 |  | 147.7 |  | 147.7
Total liabilities assumed | 648.2 |  | 648.2 |  | 648.2
Total net assets acquired | 1,274.3 |  | 1,274.3 |  | 1,274.3
APG |  |  |  |  |
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |  |  |  |
Cash and cash equivalents | 165.7 |  | 165.7 |  | 165.7
Fiduciary assets | 1,123.8 |  | 1,123.8 |  | 1,123.8
Other current assets | 1,037.2 |  | 1,037.2 |  | 1,037.2
Fixed assets | 133.9 |  | 133.9 |  | 133.9
Noncurrent assets | 234.1 |  | 234.1 |  | 234.1
Goodwill | 8,276.4 |  | 8,276.4 |  | 8,276.4
Expiration lists | 5,993.3 |  | 5,993.3 |  | 5,993.3
Non-compete agreements | 0.0 |  | 0.0 |  | 0.0
Trade names | 26.9 |  | 26.9 |  | 26.9
Total assets acquired | 16,991.3 |  | 16,991.3 |  | 16,991.3
Fiduciary liabilities | 1,123.8 |  | 1,123.8 |  | 1,123.8
Current liabilities | 867.8 |  | 867.8 |  | 867.8
Noncurrent liabilities | 1,219.8 |  | 1,219.8 |  | 1,219.8
Total liabilities assumed | 3,211.4 |  | 3,211.4 |  | 3,211.4
Total net assets acquired | 13,779.9 |  | 13,779.9 |  | 13,779.9
Twenty-two Other Acquisitions |  |  |  |  |
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items] |  |  |  |  |
Cash and cash equivalents | 25.8 |  | 25.8 |  | 25.8
Fiduciary assets | 42.8 |  | 42.8 |  | 42.8
Other current assets | 13.1 |  | 13.1 |  | 13.1
Fixed assets | 1.1 |  | 1.1 |  | 1.1
Noncurrent assets | 3.2 |  | 3.2 |  | 3.2
Goodwill | 302.5 |  | 302.5 |  | 302.5
Expiration lists | 232.3 |  | 232.3 |  | 232.3
Non-compete agreements | 4.6 |  | 4.6 |  | 4.6
Trade names | 0.0 |  | 0.0 |  | 0.0
Total assets acquired | 625.4 |  | 625.4 |  | 625.4
Fiduciary liabilities | 42.8 |  | 42.8 |  | 42.8
Current liabilities | 15.0 |  | 15.0 |  | 15.0
Noncurrent liabilities | 50.8 |  | 50.8 |  | 50.8
Total liabilities assumed | 108.6 |  | 108.6 |  | 108.6
Total net assets acquired | $ 516.8 |  | $ 516.8 |  | $ 516.8
Number of companies acquired | acquisition |  |  | 22 |  |

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