Deferred Acquisition Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Change in deferred acquisition costs
Balance at beginning of year, deferred acquisition costs	$ 2,590.0	$ 2,358.1	$ 2,442.2
Additions to deferred acquisition costs	447.0	428.9	344.4
Amortization of deferred acquisition costs	(187.1)	(94.9)	(271.4)
Adjustment related to unrealized (gains) losses on available-for-sale securities and derivative instruments	227.1	(102.1)	(157.1)
Balance at end of year, deferred acquisition costs	$ 3,077.0	$ 2,590.0	$ 2,358.1