Losses, Claims and Settlement Expenses (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense
Gross reserves at beginning of period		$ 9,929.5	$ 9,471.2
Net reserves at beginning of period				$ 6,679.7	$ 6,464.9
Provisions for insured events of the current year		632.9	620.5
Change in provision for insured events of prior years		(12.2)	(21.3)
Total incurred claims and claim adjustment expenses	[1]	620.6	599.2
Claims and claim adjustment expenses attributable to insured events of the current year		97.2	102.0
Claims and claim adjustment expenses attributable to insured events of prior years		449.7	467.3
Total payments		546.9	569.3
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		6,753.3	6,494.7
Gross reserves at end of period		9,995.9	9,488.4
Reinsurance losses recoverable
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments				3,249.7	3,006.3
Liability for Unpaid Claims and Claims Adjustment Expense
Less: reinsurance losses recoverable		3,242.5	2,993.7
General Insurance
Liability for Unpaid Claims and Claims Adjustment Expense
Net reserves at beginning of period				6,021.3	5,766.1
Provisions for insured events of the current year		598.3	584.3
Change in provision for insured events of prior years		(5.8)	(11.5)
Claims and claim adjustment expenses attributable to insured events of the current year		96.3	100.5
Claims and claim adjustment expenses attributable to insured events of prior years		418.8	426.7
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		6,098.6	5,811.6
Title Insurance
Liability for Unpaid Claims and Claims Adjustment Expense
Net reserves at beginning of period				530.9	533.4
Provisions for insured events of the current year		24.7	20.2
Change in provision for insured events of prior years		(3.1)	(5.7)
Claims and claim adjustment expenses attributable to insured events of the current year		0.1	0.1
Claims and claim adjustment expenses attributable to insured events of prior years		15.9	14.1
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		536.4	533.6
RFIG Run-off
Liability for Unpaid Claims and Claims Adjustment Expense
Net reserves at beginning of period				118.9	154.5
Provisions for insured events of the current year	[1]	6.6	11.3
Change in provision for insured events of prior years	[1]	(1.8)	(2.8)
Claims and claim adjustment expenses attributable to insured events of the current year		0.0	0.0
Claims and claim adjustment expenses attributable to insured events of prior years		13.2	24.4
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		110.4	138.5
Other
Liability for Unpaid Claims and Claims Adjustment Expense
Net reserves at beginning of period				$ 8.4	$ 10.8
Provisions for insured events of the current year		3.1	4.6
Change in provision for insured events of prior years		(1.3)	(1.2)
Claims and claim adjustment expenses attributable to insured events of the current year		0.7	1.3
Claims and claim adjustment expenses attributable to insured events of prior years		1.6	2.0
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		$ 7.8	$ 10.8

[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. 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. Estimates of coverage rescissions and claim denials are no longer material to Old Republic's consolidated financial statements.