Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Deferred Policy Acquisition Costs:
Balance, beginning of period	$ 423.0	$ 430.9	$ 454.8	$ 430.9	$ 470.1
Policy acquisition costs deferred	29.3		21.4	54.2	38.3
Costs amortized to expenses:
Recurring costs	(17.5)		(18.3)	(32.8)	(45.9)
Assumption unlocking	0.0	(0.3)	0.0	(4.0)	0.0
Realized investment gains (losses)	(3.3)		(1.9)	0.5	9.0
Offsets to net unrealized investment gains or losses included in AOCI	42.1		(14.5)	24.8	(30.0)
Balance, end of period	$ 473.6	$ 423.0	$ 441.5	$ 473.6	$ 441.5