Schedule IV - Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 8,846.4	$ 9,563.3	$ 9,523.6
Ceded Premiums Earned	2,496.7	2,310.5	2,039.0
Assumed Premiums Earned	96.2	89.4	75.1
Net premiums earned	$ 6,445.9	$ 7,342.1	$ 7,559.8
Percentage of amount assumed to net	1.50%	1.20%	1.00%
Business Intersegment, Eliminations [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 0.0	$ 0.0	$ 0.0
Ceded Premiums Earned	(0.3)	(0.3)	(0.4)
Assumed Premiums Earned	(0.3)	(0.3)	(0.4)
Net premiums earned	$ 0.0	$ 0.0	$ 0.0
Percentage of amount assumed to net	0.00%	0.00%	0.00%
Life Insurance in Force [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 933.8	$ 1,266.7	$ 1,473.2
Ceded Premiums Earned	563.3	784.5	878.5
Assumed Premiums Earned	0.0	0.0	0.0
Net premiums earned	$ 370.4	$ 482.1	$ 594.6
Percentage of amount assumed to net	0.00%	0.00%	0.00%
Life Insurance [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 6.5	$ 7.1	$ 7.8
Ceded Premiums Earned	2.6	3.2	3.0
Assumed Premiums Earned	0.0	0.0	0.0
Net premiums earned	$ 3.8	$ 3.9	$ 4.8
Percentage of amount assumed to net	0.00%	0.00%	0.00%
General Insurance [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 6,513.2	$ 6,021.0	$ 5,509.1
Ceded Premiums Earned	2,488.6	2,299.5	2,027.3
Assumed Premiums Earned	94.7	87.1	73.7
Net premiums earned	$ 4,119.2	$ 3,808.6	$ 3,555.5
Percentage of amount assumed to net	2.30%	2.30%	2.10%
Title Insurance Group [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 2,299.1	$ 3,498.1	$ 3,958.6
Ceded Premiums Earned	0.0	0.1	0.0
Assumed Premiums Earned	1.8	2.6	1.8
Net premiums earned	$ 2,300.9	$ 3,500.6	$ 3,960.5
Percentage of amount assumed to net	0.10%	0.10%	0.00%
RFIG Run-off [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 16.4	$ 23.2	$ 32.6
Ceded Premiums Earned	0.0	0.0	0.0
Assumed Premiums Earned	0.0	0.0	0.0
Net premiums earned	$ 16.4	$ 23.2	$ 32.6
Percentage of amount assumed to net	0.00%	0.00%	0.00%
Accident and health Insurance [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 11.1	$ 13.7	$ 15.2
Ceded Premiums Earned	5.8	8.0	9.0
Assumed Premiums Earned	0.0	0.0	0.0
Net premiums earned	$ 5.3	$ 5.6	$ 6.1
Percentage of amount assumed to net	0.00%	0.00%	0.00%
Life & Accident Insurance [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross amount	$ 17.6	$ 20.8	$ 23.1
Ceded Premiums Earned	8.4	11.2	12.1
Assumed Premiums Earned	0.0	0.0	0.0
Net premiums earned	$ 9.1	$ 9.6	$ 11.0
Percentage of amount assumed to net	0.00%	0.00%	0.00%