Deferred Policy Acquisition Costs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Deferred Policy Acquisition Costs:
Balance, beginning of period	$ 462.3	$ 426.2
Policy acquisition costs deferred	16.9	17.2
Costs amortized to expenses:
Recurring costs	(26.8)	(16.7)
Realized investment gains (losses)	10.5	2.7
Offsets to net unrealized investment gains or losses included in AOCI	(16.7)	4.2
Balance, end of period	$ 446.2	$ 433.6