Derivative Financial Instruments (Hedged Items In Fair Value Hedges) (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Carrying value of the hedged items, available for sale debt securities	$ 1,788,700,000	$ 2,075,100,000
Cumulative hedge accounting basis adjustment, available for sale debt securities	26,900,000	48,800,000
Carrying value of the hedged items, senior notes and long-term subordinated debt	2,745,500,000	2,745,100,000
Cumulative hedge accounting basis adjustment, senior notes and long-term subordinated debt	96,900,000	221,500,000
Carrying Value of the Hedged Items	4,534,200,000	4,820,200,000
Cumulative Hedge Accounting Basis Adjustment	123,800,000	270,300,000
Hedged asset fair value hedge discontinued cumulative increase decrease	9,800,000	10,400,000
Hedged liability fair value hedge discontinued cumulative increase decrease	$ 0	$ 0