Summary of Accounting Policies and Accounting Changes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Policyholders’ Benefits and Incurred Losses and Loss Adjustment Expenses	$ 814.9	$ 782.6	$ 825.4	$ 765.4	$ 772.8	$ 757.3	$ 499.5	$ 436.9	$ 3,188.3	$ 2,466.5	$ 1,837.4
Reinsurance recoverables	122.6				158.3				122.6	158.3
Accrued investment income	78.7				77.9				78.7	77.9
Corporate-owned life insurance	217.0				59.3				217.0	59.3
Definite-lived intangible assets	280.6				261.0				280.6	261.0
Present Value of Minimum Lease Payments	$ 0.5				1.9				$ 0.5	1.9
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									$ 21.0			$ 77.8
Value of Business Acquired
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	$ 24.1				30.2				24.1	30.2
Customer Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	4.3				6.7				4.3	6.7
Agent Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Definite-lived intangible assets	$ 62.5				$ 68.0				$ 62.5	$ 68.0
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset													$ 66.5
Present Value of Minimum Lease Payments													82.5
Deferred rent liability													$ 16.0