Basis of Presentation and Significant Accounting Policies (Narrative) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) State	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Basis Of Presentation And Significant Accounting Policies [Line Items]
Number of states company issues title insurance policies | State	49
Number of states company issues home warranty contracts | State	36
Carrying values of equity method investments	$ 102.1	$ 74.6
Loss from equity method investments	7.4	5.4	$ 11.0
Accrued Interest Receivable	14.0	24.5
Restricted cash and cash equivalents	20.7	4.0
Accrued Interest Receivable On Debt Securities	$ 38.8	$ 35.1
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Debt securities, Estimated fair value	Debt securities, Estimated fair value
Fair values of investments in debt securities for funding of statutory premium reserves and state deposits	$ 92.4	$ 107.0
Notes receivable	$ 34.4	22.4
Period of mortgage loan sold description	Collections of amounts due from mortgage loan originators occur upon sale of the underlying mortgage loans to investors in the secondary market, generally within 30 days and more typically in less than 10 days.
Debt instrument, interest rate terms	Interest is due semi-annually on March 30 and September 30, beginning March 30, 2025.
Impairment losses on property and equipment primarily related to impairments of internally developed software	$ 39.5
Impairment losses related to commercial real estate leases	$ 2.2		2.6
Assessment to determine fair value	50.00%
Escrow deposits	$ 8,900.0	10,600.0
Like-kind exchange funds	2,300.0	1,800.0
Cash deposits with third party financial institutions	901.0	830.5
Mortgage subservicing deposits interest bearing	606.5	485.7
Nonconsolidated Variable Interest Entities
Basis Of Presentation And Significant Accounting Policies [Line Items]
Carrying values of equity method investments	65.7	40.4
Loss from equity method investments	71.7
Out-of-period Adjustment
Basis Of Presentation And Significant Accounting Policies [Line Items]
Increase in other operating expenses	6.2
Increase in accounts payable and accrued liabilities	6.2
Revision of Prior Period Adjustment
Basis Of Presentation And Significant Accounting Policies [Line Items]
Decreases to retained earnings	(7.0)
Decreases to deferred income tax liabilities	(2.5)
Increase to other retirement plans liability	9.5
First American Trust
Basis Of Presentation And Significant Accounting Policies [Line Items]
Escrow deposits	4,000.0	6,300.0
Assets held-in-trust	169.4	197.1
Mortgage subservicing deposits interest bearing	606.5	485.7
Trust Assets Administered by FA Trust
Basis Of Presentation And Significant Accounting Policies [Line Items]
Assets held-in-trust	$ 4,800.0	4,400.0
Employee Stock Purchase Plan
Basis Of Presentation And Significant Accounting Policies [Line Items]
Employee stock purchase plan percentage of purchase price on closing price	85.00%
Employee stock purchase plan percentage of discount purchase price on closing price	15.00%
Capitalized Real Estate
Basis Of Presentation And Significant Accounting Policies [Line Items]
Capitalized real estate estimated useful lives, years	15 years
Minimum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of claim amounts known in the first few years of the policy life	65.00%
Minimum | Other Intangible Assets
Basis Of Presentation And Significant Accounting Policies [Line Items]
Other intangible assets estimated useful lives, years	1 year
Maximum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Percentage of claim amounts known in the first few years of the policy life	75.00%
Maximum | Other Intangible Assets
Basis Of Presentation And Significant Accounting Policies [Line Items]
Other intangible assets estimated useful lives, years	20 years
Buildings | Minimum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives, years	10 years
Buildings | Maximum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives, years	40 years
Furniture and Equipment | Minimum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives, years	1 year
Furniture and Equipment | Maximum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives, years	15 years
Leasehold Improvements
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeTermOfLeaseMember
Capitalized Software Costs | Minimum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives, years	1 year
Capitalized Software Costs | Maximum
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives, years	15 years
Title Insurance and Services and Home Warranty
Basis Of Presentation And Significant Accounting Policies [Line Items]
Goodwill, impairment loss	$ 0.0	$ 0.0	$ 0.0