Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net Income	$ 327.8	$ 394.8	$ 994.2	$ 1,180.3
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	32.3	(272.2)	170.5	(1,674.0)
Net Unrealized Gains (Losses) on Cash Flow Hedges	(0.4)	2.1	(1.1)	5.1
Net Foreign Currency Adjustments	9.6	20.2	34.2	2.6
Net Pension and Other Postretirement Benefit Adjustments	1.0	(24.5)	2.2	(83.1)
Net Change	42.5	(274.4)	205.8	(1,749.4)
Comprehensive Income (Loss)	$ 370.3	$ 120.4	$ 1,200.0	$ (569.1)