Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Statement of Cash Flows [Abstract]
Net cash provided by operating activities	$ 468.6	$ 383.8
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	1,356.1	1,612.3
Equity securities, available-for-sale	17.4	14.1
Mortgage loans on real estate	157.8	218.7
Limited partnerships/corporations	20.6	19.3
Acquisition of:
Fixed maturities	(1,878.8)	(1,586.7)
Equity securities, available-for-sale	(17.7)	0.0
Mortgage loans on real estate	(375.7)	(257.0)
Limited partnerships/corporations	(48.8)	(61.0)
Derivatives, net	(16.4)	(2.7)
Policy loans, net	6.4	2.4
Short-term investments, net	240.0	0.0
Collateral received (delivered) , net	(35.3)	102.0
Net cash (used in) provided by investing activities	(574.4)	61.4
Cash Flows from Financing Activities:
Deposits received for investment contracts	1,434.5	1,083.9
Maturities and withdrawals from investment contracts	(1,157.7)	(1,317.9)
Receipts on deposit contracts	0.0	124.7
Settlements on deposit contracts	(33.8)	(20.3)
Excess tax benefits on share-based compensation	0.6	0.0
Dividends paid and distributions of capital	(231.0)	(281.0)
Net cash provided by (used in) financing activities	12.6	(410.6)
Net (decrease) increase in cash and cash equivalents	(93.2)	34.6
Cash and cash equivalents, beginning of year	481.2	378.9
Cash and cash equivalents, end of year	$ 388.0	$ 413.5