Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net Income (Loss)	$ (76.2)	$ (75.3)	$ (245.7)	$ (14.7)
Other Comprehensive Income (Loss) Before Income Taxes:
Decrease (Increase) in Net Unrecognized Postretirement Benefit Costs	(0.2)	(0.1)	(0.3)	0.3
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax	0.0	0.1	5.9	0.3
Other Comprehensive Income (Loss), before Tax, Total	(412.5)	(80.3)	(1,638.9)	(255.3)
Other Comprehensive Income Tax Benefit (Expense)	86.7	16.7	344.2	54.2
Other Comprehensive Income (Loss), Net of Taxes	(325.8)	(63.6)	(1,294.7)	(201.1)
Total Comprehensive Income (Loss)	(402.0)	(138.9)	(1,540.4)	(215.8)
No Credit Losses Recognized in Condensed Consolidated Statements of Income (Loss)
Other Comprehensive Income (Loss) Before Income Taxes:
Changes in Net Unrealized Holding Gains (Losses) on Investment Securities with:	(411.5)	(80.8)	(1,643.2)	(254.0)
Credit Losses Recognized in Condensed Consolidated Statements of Income (Loss)
Other Comprehensive Income (Loss) Before Income Taxes:
Changes in Net Unrealized Holding Gains (Losses) on Investment Securities with:	$ (0.8)	$ 0.5	$ (1.3)	$ (1.9)