Summary of Accounting Policies and Accounting Changes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Policyholders’ Benefits and Incurred Losses and Loss Adjustment Expenses	$ 4,504.4	$ 4,600.8	$ 3,323.6
Reinsurance recoverables	39.6	41.9
Ceded reinsurance reserves	41.2	42.1
Receivables from limited liability investments or partnership investments	35.2	2.6
Accrued investment income	94.3	79.6
Equity Securities at Modified Cost	586.5	448.1
Definite-lived intangible assets	716.8	706.4
Finite-lived intangible assets, net	267.0	292.9
Retained Earnings	1,380.1	1,762.5
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(2,443.2)	$ (4,007.7)
Minimum | Cumulative Effect, Period of Adoption, Adjustment | Forecast
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained Earnings				$ 130.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest				1,000.0
Maximum | Cumulative Effect, Period of Adoption, Adjustment | Forecast
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained Earnings				230.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest				$ 1,100.0
Life Insurance | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest rate assumptions		3.00%
Life Insurance | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest rate assumptions		7.00%
Value of Business Acquired
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	237.5	$ 237.5
Finite-lived intangible assets, net	15.4	19.0
Customer Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	43.8	43.8
Finite-lived intangible assets, net	2.7	5.7
Agent Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	81.6	81.6
Finite-lived intangible assets, net	$ 50.6	$ 58.0