Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in deferred acquisition costs
Balance at beginning of year, deferred acquisition costs	$ 3,693.5	$ 3,540.7	$ 3,380.2
Costs deferred during the year	473.5	414.9	421.8
Amortization of deferred acquisition costs	(347.0)	(253.5)	(234.6)
Adjustment related to unrealized (gains) losses on available-for-sale securities and derivative instruments	(298.7)	184.9	(26.7)
Other		(193.5)
Balance at end of year, deferred acquisition costs	$ 3,521.3	$ 3,693.5	$ 3,540.7