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Contracts with Customers - Summary of Changes in Deferred Revenue Balances (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Deferred Revenue Arrangement [Line Items] |  |
Deferred revenue beginning balance | $ 706.2 | $ 609.3
Incremental deferred revenue | 396.5 | 493.0
Revenue recognized | (476.0) | (462.0)
Net change in collected billings/deposits received from customers | (44.6) | 13.0
Impact of changes in foreign exchange rates | (0.6) | 15.2
Deferred revenue recognized from business acquisitions | 22.8 | 37.7
Deferred revenue ending balance | 604.3 | 706.2
Brokerage [Member] |  |
Deferred Revenue Arrangement [Line Items] |  |
Deferred revenue beginning balance | 533.6 | 434.0
Incremental deferred revenue | 305.0 | 386.3
Revenue recognized | (389.9) | (358.4)
Net change in collected billings/deposits received from customers | (40.3) | 18.8
Impact of changes in foreign exchange rates | (0.3) | 15.2
Deferred revenue recognized from business acquisitions | 22.8 | 37.7
Deferred revenue ending balance | 430.9 | 533.6
Risk Management [Member] |  |
Deferred Revenue Arrangement [Line Items] |  |
Deferred revenue beginning balance | 172.6 | 175.3
Incremental deferred revenue | 91.5 | 106.7
Revenue recognized | (86.1) | (103.6)
Net change in collected billings/deposits received from customers | (4.3) | (5.8)
Impact of changes in foreign exchange rates | (0.3) |
Deferred revenue ending balance | $ 173.4 | $ 172.6

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- Definition Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479837/606-10-45-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479806/606-10-50-8 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479837/606-10-45-2 + Details
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- Definition Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479806/606-10-50-8 + Details
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