Derivative Financial Instruments (Hedged Items In Fair Value Hedges) (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Carrying value of the hedged items, available for sale debt securities	$ 2,631,600,000	$ 1,820,800,000
Cumulative hedge accounting basis adjustment, available for sale debt securities	(55,700,000)	(60,200,000)
Carrying value of the hedged items, senior notes and long-term subordinated debt	2,407,600,000	2,746,200,000
Cumulative hedge accounting basis adjustment, senior notes and long-term subordinated debt	(336,500,000)	(294,000,000.0)
Hedged asset fair value hedge discontinued cumulative increase decrease	2,200,000	7,300,000
Hedged liability fair value hedge discontinued cumulative increase decrease	$ 0	$ 0