Deferred Policy Acquisition Costs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Deferred Policy Acquisition Costs:
Policy acquisition costs deferred	$ 17.2	$ 24.0
Costs amortized to expenses:
Recurring costs	(16.7)	(34.3)
Realized investment gains (losses)	2.7	(6.4)
Offsets to net unrealized investment gains or losses included in AOCI	4.2	(10.7)
Change in deferred policy acquisition costs	7.4	(27.4)
Deferred policy acquisition costs, beginning of period	426.2	489.1
Deferred policy acquisition costs, end of period	$ 433.6	$ 461.7