Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Statement of Cash Flows [Abstract]
Net cash provided by operating activities	$ 678.4	$ 1,288.6
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	3,293.3	2,401.7
Equity securities, available-for-sale	0.3	49.3
Mortgage loans on real estate	351.2	302.1
Limited partnerships/corporations	59.0	39.8
Acquisition of:
Fixed maturities	(3,260.6)	(4,149.7)
Equity securities, available-for-sale	(2.1)	0.0
Mortgage loans on real estate	(964.1)	(682.2)
Limited partnerships/corporations	(87.4)	(72.6)
Derivatives, net	200.5	5.2
Policy loans, net	4.7	8.0
Short-term investments, net	28.6	0.0
Collateral received (delivered), net	(185.1)	29.9
Net cash used in investing activities	(561.7)	(2,068.5)
Cash Flows from Financing Activities:
Deposits received for investment contracts	1,910.9	2,653.1
Maturities and withdrawals from investment contracts	(1,979.5)	(1,788.4)
Settlements on deposit contracts	(48.8)	(42.8)
Dividends paid and distributions of capital	(261.0)	(274.0)
Net cash (used in) provided by financing activities	(378.4)	547.9
Net decrease in cash and cash equivalents	(261.7)	(232.0)
Cash and cash equivalents, beginning of period	561.0	661.1
Cash and cash equivalents, end of period	$ 299.3	$ 429.1