Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income	$ 313.3	$ 389.4	$ 673.9	$ 736.5
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains on Debt Securities Available for Sale	318.1	162.4	517.8	248.0
Net Unrealized Gains (Losses) on Cash Flow Hedges	(3.3)	4.8	4.0	0.5
Net Foreign Currency Adjustments	2.0	14.1	27.7	28.9
Net Pension and Other Postretirement Benefit Adjustments	8.6	4.2	15.6	16.5
Other Comprehensive Income	325.4	185.5	565.1	293.9
Comprehensive Income	$ 638.7	$ 574.9	$ 1,239.0	$ 1,030.4