Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Fair value portion of notes payable.

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Schedule 2 - Parent Company Financial Statements - Balance Sheets (Non-printing) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Feb. 24, 2015	Feb. 27, 2014
Amortized Cost of Fixed Maturity Securities	$ 6,284.5	$ 5,021.6
Senior Notes [Member] \| Senior Notes Payable, 6.00% due 2015 [Member]
Stated interest rate, percentage			6.00%
Senior Notes [Member] \| Senior Notes, 4.35 Percent Due February 15, 2025 [Member]
Stated interest rate, percentage			4.35%
Subordinated Debt [Member] \| Subordinated Debenture, 7.375 Percent Due 2054 [Member]
Stated interest rate, percentage				7.375%
Parent Company [Member]
Amortized Cost of Fixed Maturity Securities	12.6	0.3
Parent Company [Member] \| Senior Notes [Member] \| Senior Notes, 4.35 Percent Due February 15, 2025 [Member]
Fair Value of Notes Payable	$ 444.2	$ 458.1
Stated interest rate, percentage	4.35%	4.35%
Parent Company [Member] \| Subordinated Debt [Member] \| Subordinated Debenture, 7.375 Percent Due 2054 [Member]
Fair Value of Notes Payable	$ 151.1	$ 156.5
Stated interest rate, percentage	7.375%	7.375%
Parent Company [Member] \| Subordinated Debt [Member] \| Term Loan Due 2020 [Member]
Fair Value of Notes Payable	$ 35.0	$ 0.0