Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Cash Flows [Abstract]
Net cash provided by operating activities	$ 523.5	$ 241.0
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	906.7	599.4
Equity securities, available-for-sale	49.3	0.0
Mortgage loans on real estate	77.7	90.8
Limited partnerships/corporations	14.8	5.3
Acquisition of:
Fixed maturities	(1,305.5)	(927.8)
Mortgage loans on real estate	(278.5)	(242.8)
Limited partnerships/corporations	(25.2)	(10.4)
Derivatives, net	11.1	23.0
Policy loans, net	4.6	4.3
Short-term investments, net	0.0	186.1
Short-term loans to affiliates, net	(12.0)	(150.2)
Collateral received (delivered), net	58.5	13.2
Purchases of fixed assets, net	(0.1)	0.0
Net cash used in investing activities	(498.6)	(409.1)
Cash Flows from Financing Activities:
Deposits received for investment contracts	830.2	852.3
Maturities and withdrawals from investment contracts	(615.5)	(731.1)
Settlements on deposit contracts	(13.8)	(17.3)
Excess tax benefits on share-based compensation	0.1	0.6
Net cash provided by financing activities	201.0	104.5
Net increase (decrease) in cash and cash equivalents	225.9	(63.6)
Cash and cash equivalents, beginning of year	661.1	481.2
Cash and cash equivalents, end of year	$ 887.0	$ 417.6