Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 368.1	$ 313.3	$ 743.2	$ 673.9
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	100.9	318.1	(268.8)	517.8
Net Unrealized Gains (Losses) on Cash Flow Hedges	3.0	(3.3)	(2.2)	4.0
Net Foreign Currency Adjustments	2.1	2.0	7.1	27.7
Net Pension and Other Postretirement Benefit Adjustments	22.8	8.6	30.6	15.6
Net Change	128.8	325.4	(233.3)	565.1
Comprehensive Income	$ 496.9	$ 638.7	$ 509.9	$ 1,239.0