Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Income (Loss)	$ (120.5)	$ 409.9	$ 531.1
Decrease (Increase) in Net Unrecognized Postretirement Benefit Costs	(8.8)	70.2	(7.8)
Gain on Cash Flow Hedges	0.5	0.4	0.4
Other Comprehensive Income (Loss) Before Income Taxes	(294.8)	437.9	397.9
Other Comprehensive Income Tax Benefit (Expense)	62.4	(93.5)	(83.6)
Other Comprehensive Income (Loss), Net of Taxes	(232.4)	344.4	314.3
Total Comprehensive Income (Loss)	(352.9)	754.3	845.4
No Credit Losses
Changes in Net Unrealized Holding Gains (Losses) on Investment Securities	(284.5)	369.9	$ 405.3
Credit Losses
Changes in Net Unrealized Holding Gains (Losses) on Investment Securities	$ (2.0)	$ (2.6)