Summary of Significant Accounting Policies Losses, Claims and Settlement Expenses - Consolidated (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Sep. 30, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplementary Insurance Information, by Segment
Losses, claims, and settlement expenses			$ 9,929.5	$ 9,471.2	$ 9,237.6	$ 9,206.0
Liability for Unpaid Claims and Claims Adjustment Expense, Net				6,464.9	6,316.4	6,439.8
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Current Year			2,577.6	2,520.7	2,604.9
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years			(30.9)	(77.8)	(153.8)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	[1]		2,546.6	2,442.9	2,451.0
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			851.5	842.2	1,114.3
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			1,480.2	1,452.2	1,460.1
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, excluding the reclassification of Consumer Credit Indemnity coverage	[2]		2,331.7	2,294.5	2,574.4
Liability for Unpaid Claims and Claims Adjustment Expense, Net of Reinsurance Losses Recoverable			$ 6,679.7	$ 6,464.9	$ 6,316.4
One year development of consolidated reserves			0.50%	1.20%	2.40%
Three year average annual development of consolidated reserves			1.40%
General Insurance Segment [Member]
Supplementary Insurance Information, by Segment
Liability for Unpaid Claims and Claims Adjustment Expense, Net				$ 5,766.1	$ 5,471.5	5,249.9
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Current Year			$ 2,422.7	2,346.2	2,192.1
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years			14.5	(0.2)	22.7
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			835.4	813.2	765.8
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			1,346.6	1,238.1	1,227.3
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years, Excluding the Reclassification of Consumer Credit Indemnity Coverage			12.4	(6.4)	(34.5)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, excluding the reclassification of Consumer Credit Indemnity coverage			2,171.3	2,083.0	2,297.5
Liability for Unpaid Claims and Claims Adjustment Expense, Net of Reinsurance Losses Recoverable			6,021.3	5,766.1	5,471.5
RFIG Run-off Business [Member]
Supplementary Insurance Information, by Segment
Losses, claims, and settlement expenses			1.6	3.2	19.0	29.6
Liability for Unpaid Claims and Claims Adjustment Expense, Net				154.5	271.7	574.0
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Current Year	[1]		41.1	56.2	297.1
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years	[1]		(9.4)	(26.2)	(99.2)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	[2]		3.3	3.7	329.4
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	[2]		64.0	143.3	170.6
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years, Excluding the Reclassification of Consumer Credit Indemnity Coverage			(7.3)	(20.1)	(42.0)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, excluding the reclassification of Consumer Credit Indemnity coverage			78.0	115.4	195.8
Liability for Unpaid Claims and Claims Adjustment Expense, Net of Reinsurance Losses Recoverable			118.9	154.5	271.7
Increase (Decrease) in Loss and Loss Adjustment Expense Reserve, Current Year			(0.6)	(0.9)	(6.2)
Increase (Decrease) in Loss and Loss Adjustment Expense Reserve, Prior Year			0.9	12.3	3.7
Insurance Rescission			1.3	4.4	13.1
Deferred Payment Obligation		$ 657.0
Title Insurance Group [Member]
Supplementary Insurance Information, by Segment
Liability for Unpaid Claims and Claims Adjustment Expense, Net				533.4	559.7	602.0
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Current Year			99.5	96.1	95.2
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years			(32.1)	(47.7)	(74.3)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			3.6	9.1	5.0
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			66.2	65.4	58.2
Liability for Unpaid Claims and Claims Adjustment Expense, Net of Reinsurance Losses Recoverable			530.9	533.4	559.7
Corporate & Other [Member]
Supplementary Insurance Information, by Segment
Liability for Unpaid Claims and Claims Adjustment Expense, Net				10.8	13.5	13.8
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Current Year			14.1	22.1	20.4
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years			(3.9)	(3.5)	(2.9)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			9.1	16.0	13.9
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			3.3	5.2	3.9
Liability for Unpaid Claims and Claims Adjustment Expense, Net of Reinsurance Losses Recoverable			8.4	10.8	13.5
Reinsurance Recoverable Including Reinsurance Premium Paid [Member]
Supplementary Insurance Information, by Segment
Reinsurance Recoverables			$ 3,249.7	$ 3,006.3	$ 2,921.1	$ 2,766.1

[1] In common with all other insurance coverages, RFIG Run-off mortgage guaranty settled and incurred claim and claim adjustment expenses include only those costs actually or expected to be paid by the Company. As previously noted, changes in mortgage guaranty aggregate case, IBNR, and loss adjustment expense reserves entering into the determination of incurred claim costs, take into account, among a large number of variables, claim cost reductions for anticipated coverage rescissions and claims denials.
The RFIG Run-off mortgage guaranty provision for insured events of the current year was reduced by estimated coverage rescissions and claims denials of $.6, $.9 and $6.2, respectively, for 2019, 2018 and 2017. The provision for insured events of prior years in 2019, 2018 and 2017 was increased by estimated coverage rescissions and claims denials of $.9, $12.3 and $3.7, respectively. Prior year development was also affected in varying degrees by differences between actual claim settlements relative to expected experience, by reinstatement of previously rescinded or denied claims, and by subsequent revisions of assumptions in regards to claim frequency, severity or levels of associated claim settlement costs which result from consideration of underlying trends and expectations. The 2017 RFIG Run-off provision for insured events of the current year is inclusive of the claim expense provisions applicable to final settlements and probable dispositions of all known litigated and other claim costs.

[2] Rescissions reduced the Company's paid losses by an estimated $1.3, $4.4, and $13.1 for 2019, 2018, and 2017, respectively.