Summary of Significant Accounting Policies Accounting Principles (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total Common Shareholders' Equity		$ 6,000.1				$ 5,146.2				$ 6,000.1	$ 5,146.2
Net Income (Loss)		$ 275.8	$ 202.8	$ 165.5	$ 412.2	$ (106.5)	$ 275.2	$ 197.7	$ 4.0	$ 1,056.4	$ 370.5	$ 560.5
General Insurance Segment [Member]
Risk based capital		658.00%				657.00%				658.00%	657.00%
Costs and Expenses [Member]
Statutory net income amount										$ 484.5	$ (85.0)	91.0
Costs and Expenses [Member] | Significant Reconciling Items [Member]
Total statutory net income (loss)										571.6	455.6	469.2
Costs and Expenses [Member] | Deferred Policy Acquisition Costs [Member]
Statutory net income amount										9.4	17.2	11.7
Costs and Expenses [Member] | Investment adjustment [Member]
Statutory net income amount										466.3	(198.2)	0.0
Costs and Expenses [Member] | Non-admitted Assets [Member]
Statutory net income amount										0.0	0.0	0.0
Costs and Expenses [Member] | Deferred Income Taxes [Member]
Statutory net income amount										(5.8)	38.7	34.7
Costs and Expenses [Member] | Mortgage Contingency Reserves [Member]
Statutory net income amount										0.0	0.0	0.0
Costs and Expenses [Member] | Title Unearned Premiums [Member]
Statutory net income amount										25.8	23.3	27.1
Costs and Expenses [Member] | Loss Reserves [Member]
Statutory net income amount										(7.9)	38.3	40.5
Costs and Expenses [Member] | Surplus Notes [Member]
Statutory net income amount										0.0	0.0	0.0
Costs and Expenses [Member] | Sundry Adjustments [Member]
Statutory net income amount										(3.2)	(4.4)	(22.9)
Stockholders Equity [Member]
Statutory capital and surplus, balance		$ 124.7				$ (48.2)				124.7	(48.2)
Stockholders Equity [Member] | Significant Reconciling Items [Member]
Total statutory capital		5,875.0				5,194.0				5,875.0	5,194.0
Stockholders Equity [Member] | Deferred Policy Acquisition Costs [Member]
Statutory capital and surplus, balance		204.3				194.8				204.3	194.8
Stockholders Equity [Member] | Investment adjustment [Member]
Statutory capital and surplus, balance		258.1				(65.5)				258.1	(65.5)
Stockholders Equity [Member] | Non-admitted Assets [Member]
Statutory capital and surplus, balance		116.3				111.1				116.3	111.1
Stockholders Equity [Member] | Deferred Income Taxes [Member]
Statutory capital and surplus, balance		(121.8)				(63.9)				(121.8)	(63.9)
Stockholders Equity [Member] | Mortgage Contingency Reserves [Member]
Statutory capital and surplus, balance		352.5				433.1				352.5	433.1
Stockholders Equity [Member] | Title Unearned Premiums [Member]
Statutory capital and surplus, balance		571.7				545.8				571.7	545.8
Stockholders Equity [Member] | Loss Reserves [Member]
Statutory capital and surplus, balance		(449.3)				(440.4)				(449.3)	(440.4)
Stockholders Equity [Member] | Surplus Notes [Member]
Statutory capital and surplus, balance		(808.0)				(744.5)				(808.0)	(744.5)
Stockholders Equity [Member] | Sundry Adjustments [Member]
Statutory capital and surplus, balance		0.7				(18.6)				0.7	(18.6)
Insurance Subsidiaries [Member] | Costs and Expenses [Member]
Total statutory net income (loss)	[1]									418.4	446.8	529.1
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | General Insurance Segment [Member]
Total statutory net income (loss)	[1]									332.2	290.5	348.9
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | Title Insurance Group [Member]
Total statutory net income (loss)	[1]									145.1	110.5	127.9
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | RFIG Run-off Business [Member]
Total statutory net income (loss)	[1]									(62.8)	44.9	50.5
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | Life & Health Insurance [Member]
Total statutory net income (loss)	[1]									3.9	0.9	1.8
Insurance Subsidiaries [Member] | Stockholders Equity [Member]
Total statutory capital	[1]	5,030.0				4,478.2				5,030.0	4,478.2
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | General Insurance Segment [Member]
Total statutory capital	[1]	4,263.5				3,847.3				4,263.5	3,847.3
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | Title Insurance Group [Member]
Total statutory capital	[1]	599.0				503.1				599.0	503.1
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | RFIG Run-off Business [Member]
Total statutory capital	[1]	120.7				88.0				120.7	88.0
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | Life & Health Insurance [Member]
Total statutory capital	[1]	46.8				39.8				46.8	39.8
NonInsurance Subsidiaries [Member] | Costs and Expenses [Member] | Significant Reconciling Items [Member]
Total statutory net income (loss)										153.2	8.8	$ (59.9)
NonInsurance Subsidiaries [Member] | Stockholders Equity [Member] | Significant Reconciling Items [Member]
Total statutory capital		$ 844.9				$ 715.8				$ 844.9	$ 715.8

[1] (a)    The insurance laws of the respective states in which the Company’s insurance subsidiaries are incorporated prescribe minimum capital and surplus requirements for the lines of business they are licensed to write. For domestic property and casualty and life and accident insurance companies the National Association of Insurance Commissioners also prescribes risk-based capital ("RBC") requirements. The RBC is a measure of statutory capital in relationship to a formula-driven definition of risk relative to a company’s balance sheet and mix of business. The combined RBC ratio of our primary General insurance subsidiaries was 658% and 657% of the company action level RBC at December 31, 2019 and 2018, respectively. The minimum capital requirements for the Company’s Title Insurance subsidiaries are established by statute in the respective states of domicile. The minimum regulatory capital requirements are not significant in relationship to the recorded statutory capital of the Company’s Title and Life & Accident insurance subsidiaries. At December 31, 2019 and 2018 each of the Company’s General, Title, RFIG and Life and Accident insurance subsidiaries exceeded the minimum statutory capital and surplus requirements. Refer to Note 1(s) - Regulatory Matters for a discussion regarding the RFIG Run-off group.