Trust Assets, Escrow and Other Deposits (Narrative) (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Other Assets [Line Items]
Escrow deposits	$ 9,800.0	$ 8,900.0
Assets held-in-trust	4,900.0	4,800.0
Like-kind exchange funds	1,800.0	2,300.0
Cash deposits	1,100.0	901.0
First American Trust
Other Assets [Line Items]
Escrow deposits	4,300.0	4,000.0
Assets held-in-trust	193.2	169.4
Cash deposits	$ 764.7	$ 606.5

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