Information About Segments of Business (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
Segment Reporting Information
Concentration Risk, Percentage										10.00%
Consolidated Revenues [Abstract]
Net premiums earned										$ 5,498.3	$ 5,253.4	$ 5,080.2
Title, escrow and other fees										495.9	450.5	459.5
Sub-total										5,994.2	5,703.9	5,539.7
Total operating revenues										6,577.6	6,257.4	6,051.5
Consolidated net realized investment gains (losses)										636.1	(235.6)	211.6
Consolidated revenues		$ 1,929.3	$ 1,771.0	$ 1,644.7	$ 1,868.6	$ 1,280.9	$ 1,779.7	$ 1,630.7	$ 1,330.4	7,213.7	6,021.8	6,263.1
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Consolidated net realized investment gains (losses)										636.1	(235.6)	211.6
Consolidated income (loss) before income taxes (credits)										1,322.4	438.1	725.4
Realized from actual transactions and impairments										36.6	58.2	211.6
Consolidated Income Tax Expense (Credits) [Abstract]
Income tax expense (credits)										265.9	67.5	164.8
Income tax expense (credits) on consolidated net realized investment gains (losses)	[1],[2]									133.8	(49.6)	(30.8)
Consolidated assets [Abstract]
Assets		21,076.3				19,327.1				21,076.3	19,327.1
Unrealized from changes in fair value of equity securities										599.5	(293.8)	0.0
General Insurance Group [Member]
Consolidated Revenues [Abstract]
Net premiums earned	[3]									3,432.4	3,277.1	3,110.8
Net investment income and other income	[3]									488.4	462.3	420.8
Total operating revenues	[3]									3,920.8	3,739.4	3,531.6
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Income (loss) before income taxes (credits) and realized investment gains or losses	[3],[4]									370.2	363.9	340.3
Interest charges on intercompany financing arrangements										71.5	68.0	57.2
Consolidated Income Tax Expense (Credits) [Abstract]
Income tax expense (credits)	[3]									69.9	62.6	170.6
Consolidated assets [Abstract]
Assets		17,870.0				16,411.4				17,870.0	16,411.4
Title Insurance Group [Member]
Consolidated Revenues [Abstract]
Net premiums earned										1,993.2	1,885.6	1,827.6
Title, escrow and other fees										495.9	450.5	459.5
Sub-total										2,489.2	2,336.1	2,287.2
Net investment income and other income										42.1	39.2	37.8
Total operating revenues										2,531.3	2,375.4	2,325.0
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Income (loss) before income taxes (credits) and realized investment gains or losses	[4]									230.8	219.3	237.1
Interest charges on intercompany financing arrangements										5.5	6.1	7.8
Consolidated Income Tax Expense (Credits) [Abstract]
Income tax expense (credits)										49.5	46.2	79.7
Consolidated assets [Abstract]
Assets		1,695.0				1,452.2				1,695.0	1,452.2
RFIG Run-off Business [Member]
Consolidated Revenues [Abstract]
Net premiums earned	[3]									59.2	75.9	122.9
Net investment income and other income	[3]									17.6	20.1	21.7
Total operating revenues	[3]									76.8	96.1	144.6
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Income (loss) before income taxes (credits) and realized investment gains or losses	[3],[5]									30.3	49.9	(73.5)
Consolidated Income Tax Expense (Credits) [Abstract]
Income tax expense (credits)	[3]									5.8	10.1	(77.0)
Consolidated assets [Abstract]
Assets		615.1				736.7				615.1	736.7
Additional claim and related expenses												130.0
Total of major segments [Member]
Consolidated Revenues [Abstract]
Consolidated revenues										6,529.1	6,211.0	6,001.4
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Consolidated income (loss) before income taxes (credits)										631.4	633.2	503.9
Consolidated Income Tax Expense (Credits) [Abstract]
Income tax expense (credits)										125.3	119.0	173.3
Consolidated assets [Abstract]
Assets		20,180.2				18,600.3				20,180.2	18,600.3
Other sources - net [Member]
Consolidated Revenues [Abstract]
Consolidated revenues	[6]									170.0	169.1	170.3
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Consolidated income (loss) before income taxes (credits)	[6]									54.8	40.4	9.9
Consolidated Income Tax Expense (Credits) [Abstract]
Income tax expense (credits)	[6]									6.6	(1.8)	22.4
Consolidated assets [Abstract]
Assets	[6]	1,095.4				1,028.9				1,095.4	1,028.9
Consolidation elimination adjustments [Member]
Consolidated Revenues [Abstract]
Net premiums earned										0.0	0.0	0.0
Consolidated revenues										(121.4)	(122.7)	$ (120.1)
Consolidated assets [Abstract]
Assets		$ (199.3)				$ (302.2)				$ (199.3)	$ (302.2)

[1] (b)    Reflects primarily the combination of fully taxable investment gains or losses.

[2] $104.9, for 2017, of deferred income tax credits to adjust to the new 21% tax rate of 2018 pertaining to unrealized gains (losses) as of December 31, 2017. Deferred income taxes on unrealized gains (losses) would normally be a part of the statement of comprehensive income rather than the income statement.

[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] Segment pretax operating income (loss) is reported net of interest charges on intercompany financing arrangements with Old Republic's holding company parent for the following segments: General - $71.5, $68.0 and $57.2 for the years ended December 31, 2019, 2018, and 2017, respectively; Title - $5.5, $6.1 and $7.8 for the years ended December 31, 2019, 2018, and 2017, respectively.

[5] RFIG Run-off segment pretax operating income (loss) for 2017 include additional claim and related expense provisions of $130.0. These costs apply to the final settlements and probable dispositions of all known litigated and other claim costs incurred by the Company's run-off Financial Indemnity business during the Great Recession years and their aftermath.

[6] Includes amounts for a small life and accident insurance business as well as those of the parent holding company and its internal corporate services subsidiaries.