Information About Segments of Business (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Consolidated Revenues [Abstract]
Net premiums earned										$ 6,445.9	$ 7,342.1	$ 7,559.8
Title, escrow and other fees										261.8	333.2	443.8
Sub-total										6,707.7	7,675.3	8,003.6
Total operating revenues										7,449.3	8,284.9	8,583.5
Consolidated net realized investment gains (losses)										(67.0)	62.2	6.9
Consolidated revenues		$ 1,941.1	$ 1,760.1	$ 1,798.3	$ 1,758.7	$ 2,345.5	$ 1,721.0	$ 1,810.3	$ 2,206.6	7,258.3	8,083.7	9,341.6
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Consolidated net realized investment gains (losses)										(67.0)	62.2	6.9
Consolidated income (loss) before income taxes (credits)										747.4	857.4	1,922.1
Consolidated Income Tax Expense (Credits) [Abstract]
Income tax expense (credits)										148.7	170.9	387.7
Income tax expense (credits) on consolidated net realized investment gains (losses)										(40.0)	(42.5)	159.6
Consolidated assets [Abstract]
Assets		26,501.4				25,159.4				26,501.4	25,159.4
Unrealized from changes in fair value of equity securities										(123.9)	(263.4)	751.1
Gain (Loss) on Investments										(190.9)	(201.1)	758.0
Unrealized from changes in fair value of equity securities										(123.9)	(263.4)	751.1
Corporate, Non-Segment
Consolidated Revenues [Abstract]
Consolidated revenues	[1]									208.0	195.5	166.6
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Consolidated income (loss) before income taxes (credits)	[1]									(4.2)	24.6	25.7
Consolidated assets [Abstract]
Assets	[1]	1,912.9				1,736.8				1,912.9	1,736.8
Consolidation elimination adjustments [Member]
Consolidated Revenues [Abstract]
Net premiums earned										0.0	0.0	0.0
Consolidated revenues										(146.5)	(138.9)	(119.0)
Consolidated assets [Abstract]
Assets		(303.2)				(227.2)				(303.2)	(227.2)
General Insurance Group [Member] | Operating Segments
Consolidated Revenues [Abstract]
Net premiums earned										4,119.2	3,808.6	3,555.5
Net investment income and other income										625.0	507.0	486.9
Total operating revenues										4,744.3	4,315.6	4,042.5
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Income (loss) before income taxes (credits) and realized investment gains or losses	[2]									787.8	689.8	589.6
Consolidated assets [Abstract]
Assets		22,710.5				21,227.9				22,710.5	21,227.9
Title Insurance Group [Member] | Operating Segments
Consolidated Revenues [Abstract]
Net premiums earned										2,300.9	3,500.6	3,960.5
Title, escrow and other fees										261.8	333.2	443.8
Sub-total										2,562.8	3,833.8	4,404.3
Net investment income and other income										57.8	48.8	44.9
Total operating revenues										2,620.6	3,882.7	4,449.3
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Income (loss) before income taxes (credits) and realized investment gains or losses	[2]									133.5	308.8	515.7
Consolidated assets [Abstract]
Assets		1,948.2				2,077.6				1,948.2	2,077.6
RFIG Run-off [Member] | Operating Segments
Consolidated Revenues [Abstract]
Net premiums earned										16.4	23.2	32.6
Net investment income and other income										6.3	6.7	11.4
Total operating revenues										22.7	30.0	44.1
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Income (loss) before income taxes (credits) and realized investment gains or losses										21.2	35.2	32.8
Consolidated assets [Abstract]
Assets	[3]	232.8				344.2				232.8	344.2
Total of major segments [Member] | Operating Segments
Consolidated Revenues [Abstract]
Consolidated revenues										7,387.8	8,228.3	8,536.0
Consolidated Income (Loss) Before Taxes (Credits) [Abstract]
Consolidated income (loss) before income taxes (credits)										942.6	1,033.9	$ 1,138.2
Consolidated assets [Abstract]
Assets		$ 24,891.7				$ 23,649.9				$ 24,891.7	$ 23,649.9

[1] 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

[2] Segment pretax operating income is reported net of interest charges on intercompany financing arrangements with Old Republic's holding company parent for the following segments: General - $76.5, $68.9, and $63.5 for the years ended December 31, 2023, 2022, and 2021, respectively; Title - $–, $0.8, and $1.9 for the years ended December 31, 2023, 2022, and 2022, respectively.

[3] At December 31, 2023, the Company classified its RFIG Run-off mortgage insurance business as held-for-sale in its consolidated balance sheet. See Note 2 for further discussion.