Summary of Significant Accounting Policies Accounting Principles (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018		Jan. 01, 2020
Total Common Shareholders' Equity		$ 6,186.6				$ 6,000.1				$ 6,186.6	$ 6,000.1
Net Income (Loss)		519.7	$ 246.0	$ 397.7	$ (604.8)	275.8	$ 202.8	$ 165.5	$ 412.2	558.6	1,056.4		$ 370.5
Retained earnings		$ 4,394.8				$ 4,386.0				4,394.8	4,386.0
Net premiums earned										6,345.8	5,919.9	[1]	5,651.1	[1]
Title, escrow, and other fees										391.9	321.1		289.8
Underwriting Acquisition And Other Expenses										$ 3,942.4	3,525.4		3,317.7
Revision of Prior Period, Accounting Standards Update, Adjustment | Accounting Standards Update 2016-13
Retained earnings															$ 2.3
Revision of Prior Period, Adjustment
Net premiums earned											421.5		397.7
Title, escrow, and other fees											174.7		160.6
Underwriting Acquisition And Other Expenses											$ 246.8		237.0
General Insurance Segment [Member]
Risk based capital		625.00%				658.00%				625.00%	658.00%
Title Insurance Group [Member]
Net premiums earned	[2]									$ 2,894.4	$ 2,414.8		2,283.3
Title, escrow, and other fees	[2]									391.9	321.1		289.8
RFIG Run-off Business [Member]
Net premiums earned	[3]									45.1	59.2		75.9
Costs and Expenses [Member] | Significant Reconciling Items [Member]
Total statutory net income (loss)										501.0	571.6		455.6
Costs and Expenses [Member] | Deferred Policy Acquisition Costs [Member]
Statutory net income amount										7.4	9.4		17.2
Costs and Expenses [Member] | Investment adjustment [Member]
Statutory net income amount										4.5	466.3		(198.2)
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										23.6	(5.8)		38.7
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										53.9	25.8		23.3
Costs and Expenses [Member] | Loss Reserves [Member]
Statutory net income amount										(24.8)	(7.9)		38.3
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										(7.3)	(3.2)		(4.4)
Costs and Expenses [Member] | Adjustment to US-GAAP
Statutory net income amount										57.5	484.5		(85.0)
Stockholders Equity [Member] | Significant Reconciling Items [Member]
Total statutory capital		$ 5,814.2				$ 5,875.0				5,814.2	5,875.0
Stockholders Equity [Member] | Deferred Policy Acquisition Costs [Member]
Statutory capital and surplus, balance		211.7				204.3				211.7	204.3
Stockholders Equity [Member] | Investment adjustment [Member]
Statutory capital and surplus, balance		589.7				258.1				589.7	258.1
Stockholders Equity [Member] | Non-admitted Assets [Member]
Statutory capital and surplus, balance		139.0				116.3				139.0	116.3
Stockholders Equity [Member] | Deferred Income Taxes [Member]
Statutory capital and surplus, balance		(203.0)				(121.8)				(203.0)	(121.8)
Stockholders Equity [Member] | Mortgage Contingency Reserves [Member]
Statutory capital and surplus, balance		316.7				352.5				316.7	352.5
Stockholders Equity [Member] | Title Unearned Premiums [Member]
Statutory capital and surplus, balance		625.6				571.7				625.6	571.7
Stockholders Equity [Member] | Loss Reserves [Member]
Statutory capital and surplus, balance		(474.8)				(449.3)				(474.8)	(449.3)
Stockholders Equity [Member] | Surplus Notes [Member]
Statutory capital and surplus, balance		(841.5)				(808.0)				(841.5)	(808.0)
Stockholders Equity [Member] | Sundry Adjustments [Member]
Statutory capital and surplus, balance		8.8				0.7				8.8	0.7
Stockholders Equity [Member] | Adjustment to US-GAAP
Statutory capital and surplus, balance		372.2				124.7				372.2	124.7
Insurance Subsidiaries [Member] | Costs and Expenses [Member]
Total statutory net income (loss)	[4]									472.8	418.4		446.8
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | General Insurance Segment [Member]
Total statutory net income (loss)	[4]									285.0	332.2		290.5
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | Title Insurance Group [Member]
Total statutory net income (loss)	[4]									182.6	145.1		110.5
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | RFIG Run-off Business [Member]
Total statutory net income (loss)	[4]									1.9	(62.8)		44.9
Insurance Subsidiaries [Member] | Costs and Expenses [Member] | Life & Health Insurance [Member]
Total statutory net income (loss)	[4]									3.3	3.9		0.9
Insurance Subsidiaries [Member] | Stockholders Equity [Member]
Total statutory capital	[4]	5,061.1				5,030.0				5,061.1	5,030.0
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | General Insurance Segment [Member]
Total statutory capital	[4]	4,244.0				4,263.5				4,244.0	4,263.5
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | Title Insurance Group [Member]
Total statutory capital	[4]	648.3				599.0				648.3	599.0
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | RFIG Run-off Business [Member]
Total statutory capital	[4]	118.5				120.7				118.5	120.7
Insurance Subsidiaries [Member] | Stockholders Equity [Member] | Life & Health Insurance [Member]
Total statutory capital	[4]	50.3				46.8				50.3	46.8
NonInsurance Subsidiaries [Member] | Costs and Expenses [Member] | Significant Reconciling Items [Member]
Total statutory net income (loss)										28.4	153.2		$ 8.8
NonInsurance Subsidiaries [Member] | Stockholders Equity [Member] | Significant Reconciling Items [Member]
Total statutory capital		$ 753.1				$ 844.9				$ 753.1	$ 844.9

[1] Certain reclassifications were made to net premiums earned, title, escrow, and other fees, and underwriting, acquisition, and other expenses in 2019 and 2018 to conform to the presentation adopted in 2020.

[2] (d)    Reclassification adjustments were made to certain Title segment revenues and expenses in prior periods to conform to the presentation adopted in 2020. See Note 1(c).

[3] (a) Results for the Consumer Credit Indemnity ("CCI") run-off business are expected to be immaterial in the remaining run-off periods. Effective July 1, 2019, these results have been reclassified to the General Insurance segment for all future periods. Previously these results were reflected as part of the RFIG Run-off Business.

[4] (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 625% and 658% of the company action level RBC at December 31, 2020 and 2019, 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, 2020 and 2019 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.