Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Statement of Cash Flows [Abstract]
Net cash provided by operating activities	$ 1,312.4	$ 732.3
Proceeds from the sale, maturity, disposal or redemption of:
Fixed maturities	2,413.2	2,215.0
Equity securities, available-for-sale	17.4	14.1
Mortgage loans on real estate	345.7	314.1
Limited partnerships/corporations	31.1	34.9
Acquisition of:
Fixed maturities	(3,685.6)	(2,290.6)
Equity securities, available-for-sale	(28.0)	0.0
Mortgage loans on real estate	(700.1)	(482.6)
Limited partnerships/corporations	(72.6)	(93.2)
Derivatives, net	(55.8)	(22.9)
Policy loans, net	5.5	1.8
Short-term investments, net	241.5	(6.3)
Collateral received (delivered), net	52.1	103.2
Net cash used in investing activities	(1,435.6)	(212.5)
Cash Flows from Financing Activities:
Deposits received for investment contracts	2,317.5	1,669.9
Maturities and withdrawals from investment contracts	(1,756.6)	(1,946.3)
Receipts on deposit contracts	0.0	124.7
Settlements on deposit contracts	(49.4)	(36.2)
Excess tax benefits on share-based compensation	0.7	0.0
Dividends paid and distributions of capital	(231.0)	(281.0)
Net cash provided by (used in) financing activities	281.2	(468.9)
Net increase in cash and cash equivalents	158.0	50.9
Cash and cash equivalents, beginning of year	481.2	378.9
Cash and cash equivalents, end of year	$ 639.2	$ 429.8