Supplemental Disclosures of Cash Flow Information - Cash Equivalents, Restricted Cash and Fiduciary Cash (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents - non-restricted cash	$ 1,165.0		$ 1,792.4
Cash and cash equivalents - restricted cash	234.3		230.0
Total cash and cash equivalents	1,399.3	$ 14,987.3	2,022.4
Fiduciary cash	6,941.0	$ 5,481.3	6,272.6
Total cash, cash equivalents, restricted cash and fiduciary cash	$ 8,340.3		$ 8,295.0

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-8

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 24
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-24

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-4

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant