Losses, Claims and Settlement Expenses (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2020	Jun. 30, 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		1,255.7	1,253.9
Change in provision for insured events of prior years		(17.0)	(24.5)
Total incurred claims and claim adjustment expenses	[1]	1,238.6	1,229.3
Claims and claim adjustment expenses attributable to insured events of the current year		285.9	307.1
Claims and claim adjustment expenses attributable to insured events of prior years		744.2	837.4
Total payments		1,030.2	1,144.6
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		6,888.1	6,549.6
Gross reserves at end of period		10,230.9	9,636.3
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		3,342.7	3,086.7
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		1,178.7	1,181.3
Change in provision for insured events of prior years		(4.9)	(7.1)
Claims and claim adjustment expenses attributable to insured events of the current year		282.5	301.2
Claims and claim adjustment expenses attributable to insured events of prior years		696.5	758.1
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		6,216.0	5,880.8
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		50.1	44.0
Change in provision for insured events of prior years		(10.7)	(11.4)
Claims and claim adjustment expenses attributable to insured events of the current year		0.9	0.7
Claims and claim adjustment expenses attributable to insured events of prior years		25.3	31.7
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		544.0	533.5
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]	21.0	20.2
Change in provision for insured events of prior years	[1]	0.6	(4.3)
Claims and claim adjustment expenses attributable to insured events of the current year		0.1	0.2
Claims and claim adjustment expenses attributable to insured events of prior years		20.4	45.0
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		119.9	125.1
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		5.8	8.2
Change in provision for insured events of prior years		(1.9)	(1.5)
Claims and claim adjustment expenses attributable to insured events of the current year		2.3	4.8
Claims and claim adjustment expenses attributable to insured events of prior years		1.9	2.5
Amount of reserves for unpaid claims and claim adjustment expenses at the end of each period, net of reinsurance losses recoverable		$ 8.1	$ 10.0

[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.