Deferred Policy Acquisition Costs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Deferred Policy Acquisition Costs:
Balance, beginning of period	$ 446.2	$ 433.6	$ 462.3	$ 426.2
Policy acquisition costs deferred	20.3	16.4	37.2	33.5
Costs amortized to expenses:
Recurring costs	(15.0)	(21.3)	(41.8)	(38.0)
Realized investment gains (losses)	(1.4)	(5.3)	9.1	(2.6)
Offsets to net unrealized investment gains or losses included in AOCI	(14.5)	39.7	(31.2)	44.0
Balance, end of period	$ 435.6	$ 463.1	$ 435.6	$ 463.1