Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in deferred acquisition costs
Balance at beginning of year, deferred acquisition costs	$ 2,993.0	$ 3,077.0	$ 2,590.0
Additions to deferred acquisition costs	390.3	404.1	447.0
Amortization of deferred acquisition costs	(270.8)	(367.2)	(187.1)
Adjustment related to unrealized (gains) losses on available-for-sale securities and derivative instruments	164.5	(120.9)	227.1
Other	(0.9)
Balance at end of year, deferred acquisition costs	$ 3,276.1	$ 2,993.0	$ 3,077.0