Derivative Financial Instruments (Hedged Items In Fair Value Hedges) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Carrying value of the hedged items, available for sale debt securities	$ 7,779.7	$ 5,048.8
Cumulative hedge accounting basis adjustment, available for sale debt securities	171.9	77.5
Carrying value of the hedged items, senior notes and long-term subordinated debt	2,554.9	2,495.9
Cumulative hedge accounting basis adjustment, senior notes and long-term subordinated debt	(190.3)	(248.7)
Hedged asset fair value hedge discontinued cumulative increase decrease	1.9	2.2
Hedged liability fair value hedge discontinued cumulative increase decrease	$ 17.7	$ 29.6