Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Statement of Cash Flows [Abstract]
Net cash provided by operating activities	$ 1,288.5	$ 1,312.4
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	2,401.7	2,413.2
Equity securities, available-for-sale	49.3	17.4
Mortgage loans on real estate	302.1	345.7
Limited partnerships/corporations	39.8	31.1
Acquisition of:
Fixed maturities	(4,149.7)	(3,685.6)
Equity securities, available-for-sale	0.0	(28.0)
Mortgage loans on real estate	(682.2)	(700.1)
Limited partnerships/corporations	(72.6)	(72.6)
Derivatives, net	5.2	(55.8)
Policy loans, net	8.0	5.5
Short-term investments, net	0.0	241.5
Collateral received (delivered), net	29.9	52.1
Net cash used in investing activities	(2,068.5)	(1,435.6)
Cash Flows from Financing Activities:
Deposits received for investment contracts	2,653.1	2,317.5
Maturities and withdrawals from investment contracts	(1,788.4)	(1,756.6)
Settlements on deposit contracts	(42.8)	(49.4)
Excess tax benefits on share-based compensation	0.1	0.7
Dividends paid and distributions of capital	(274.0)	(231.0)
Net cash provided by financing activities	548.0	281.2
Net (decrease) increase in cash and cash equivalents	(232.0)	158.0
Cash and cash equivalents, beginning of year	661.1	481.2
Cash and cash equivalents, end of year	$ 429.1	$ 639.2