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Summary of Accounting Policies and Accounting Changes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Policyholders’ Benefits and Incurred Losses and Loss Adjustment Expenses	$ 863.4	$ 877.5	$ 747.5	$ 835.2	$ 814.9	$ 782.6	$ 825.4	$ 765.4	$ 3,323.6	$ 3,188.3	$ 2,466.5
Reinsurance recoverables	50.1				122.6				50.1	122.6
Accrued investment income	77.1				78.7				77.1	78.7
Company-owned Life Insurance	327.4				217.0				327.4	217.0
Definite-lived intangible assets	607.5				569.5				607.5	569.5
Present Value of Minimum Lease Payments	0.2								0.2
Finite-lived intangible assets, net	$ 272.3				280.6				$ 272.3	280.6
Life Insurance \| Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest rate assumptions	3.00%								3.00%
Life Insurance \| Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest rate assumptions	7.00%								7.00%
Change in Accounting Estimate, Use of Death Master File in Reserving Process
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Policyholders’ Benefits and Incurred Losses and Loss Adjustment Expenses												$ 77.8
Value of Business Acquired
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	$ 194.5				194.5				$ 194.5	194.5
Finite-lived intangible assets, net	20.3				24.1				20.3	24.1
Customer Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	39.0				39.0				39.0	39.0
Finite-lived intangible assets, net	3.4				4.3				3.4	4.3
Agent Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	74.4				74.4				74.4	74.4
Finite-lived intangible assets, net	$ 57.6				$ 62.5				$ 57.6	$ 62.5