Trust Assets, Escrow and Other Deposits (Narrative) (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Other Assets [Line Items]
Escrow deposits	$ 9,000.0	$ 10,600.0
Assets held-in-trust	4,800.0	4,400.0
Like-kind exchange funds	2,000.0	1,800.0
Cash deposits	1,200.0	830.5
First American Trust
Other Assets [Line Items]
Escrow deposits	4,600.0	6,300.0
Assets held-in-trust	155.2	197.1
Cash deposits	$ 882.7	$ 485.7

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 440
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478522/954-440-50-1

Name:	us-gaap_EscrowDeposit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant