Deferred Acquisition Costs (Schedule of Deferred Acquisition Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	$ 8,811.0	$ 7,393.5	$ 6,121.5
Costs deferred	4,528.7	4,685.5	4,028.4
Amortization	(3,662.6)	(3,268.0)	(2,756.4)
Ending balance	$ 9,677.1	$ 8,811.0	$ 7,393.5