Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net Income	$ 126.1	$ 122.1	$ 190.1	$ 277.4
Other Comprehensive Income (Loss) Before Income Taxes:
Decrease in Net Unrecognized Postretirement Benefit Costs	0.7	0.0	1.4	0.6
Gain on Cash Flow Hedges	0.0	0.0	0.1	0.1
Other Comprehensive Income (Loss) Before Income Taxes	408.0	159.3	204.0	322.8
Other Comprehensive Income Tax Benefit (Expense)	(85.6)	(33.3)	(42.8)	(67.7)
Other Comprehensive Income (Loss)	322.4	126.0	161.2	255.1
Total Comprehensive Income (Loss)	448.5	248.1	351.3	532.5
No Credit Losses Recognized in Consolidated Statements of Income
Other Comprehensive Income (Loss) Before Income Taxes:
Changes in Net Unrealized Holding Gains (Losses) on Investment Securities with:	408.1	159.3	206.2	322.1
Credit Losses Recognized in Consolidated Statements of Income
Other Comprehensive Income (Loss) Before Income Taxes:
Changes in Net Unrealized Holding Gains (Losses) on Investment Securities with:	$ (0.8)	$ 0.0	$ (3.7)	$ 0.0