Deferred Policy Acquisition Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change in deferred policy acquisition costs
Balance at beginning of year, deferred policy acquisition costs	$ 3,529.8	$ 3,681.4	$ 4,153.0
Additions to deferred policy acquisition costs	520.5	496.3	482.4
Amortization of deferred policy acquisition costs	(538.0)	(205.9)	(92.2)
Adjustment related to unrealized (gains) losses on available-for-sale securities and derivative instruments	(198.8)	(442.0)	(861.8)
Balance at end of year, deferred policy acquisition costs	$ 3,313.5	$ 3,529.8	$ 3,681.4