Deferred Costs, Capitalized, Prepaid, and Other Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Costs	$ 622.2	$ 683.8	$ 635.6	$ 688.0
Deferred Policy Acquisition Cost, Capitalization	449.3	530.0
Deferred Policy Acquisition Costs, Amortization Expense	(453.8)	(528.7)
Deferred Policy Acquisition Cost, Experience Adjustment	$ (8.9)	(5.5)
Disposal Group, Held-for-sale, Not Discontinued Operations
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Disposal Group, Including Discontinued Operation, Deferred Policy Acquisition Cost		38.7
Disposal Group, Held-for-sale, Not Discontinued Operations | Reserve National Insurance Company
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Disposal Group, Including Discontinued Operation, Deferred Policy Acquisition Cost		38.7
Effect of Retrospective Application of Accounting Standards Update 2018-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Liability for Future Policy Benefit, Weighted-Average Duration	13 years 9 months 18 days		15 years 6 months
Term Life Insurance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Cost, Capitalization	$ 42.2	47.0
Deferred Policy Acquisition Costs, Amortization Expense	(14.7)	(21.5)
Deferred Policy Acquisition Cost, Experience Adjustment	(8.9)	(5.5)
Property and Casualty Insurance Reserves
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Costs	199.1	244.5	$ 231.1	268.7
Deferred Policy Acquisition Cost, Capitalization	407.1	483.0
Deferred Policy Acquisition Costs, Amortization Expense	(439.1)	(507.2)
Deferred Policy Acquisition Cost, Experience Adjustment	0.0	0.0
Life Insurance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Policy Acquisition Costs	$ 423.1	$ 439.3	$ 404.5	$ 419.3