Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 375.1	$ 360.6
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Debt Securities Available for Sale	(369.7)	199.7
Net Unrealized Gains (Losses) on Cash Flow Hedges	(5.2)	7.3
Net Foreign Currency Adjustments	5.0	25.7
Net Pension and Other Postretirement Benefit Adjustments	7.8	7.0
Net Change	(362.1)	239.7
Comprehensive Income	$ 13.0	$ 600.3