Investments (Unrealized Gains and Losses on Available-For-Sale and Other Securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Benefit (provision) for deferred income taxes	$ 217.9	$ 58.9	$ (68.1)
Net Unrealized Appreciation (Depreciation) on Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Net appreciation (depreciation), beginning of year	184.9
Net appreciation (depreciation), end of year		184.9
Fixed Maturities [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Net appreciation (depreciation), beginning of year	184.9	428.1	216.0
Net appreciation (depreciation) on available-for-sale fixed maturities	(1,044.2)	(302.1)	280.2
Benefit (provision) for deferred income taxes	217.9	58.9	(68.1)
Total adjustment	(826.3)	(243.2)	212.1
Net appreciation (depreciation), end of year	$ (641.4)	$ 184.9	$ 428.1