Deferred Acquisition Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Change in deferred acquisition costs
Balance at beginning of year, deferred acquisition costs	$ 4,340.3	$ 3,581.2	$ 3,757.5	$ 3,409.7
Costs deferred during the year	87.5	118.0	285.5	355.1
Amortization of deferred acquisition costs	4.0	(34.3)	(326.5)	(192.8)
Adjustment related to unrealized (gains) losses on available-for-sale securities and derivative instruments	402.2	32.0	1,117.5	124.9
Balance at end of year, deferred acquisition costs	$ 4,834.0	$ 3,696.9	$ 4,834.0	$ 3,696.9