Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Gain (Loss)	$ (13.8)	$ 84.6
Credit Losses on Fixed Maturity Securities	4.1	8.3
Loss on Benefits and Change in Reserves for Future Benefits	(1,843.9)	(2,051.2)
Net Investment Income	527.2	548.7
Other Expenses	(243.8)	(245.0)
Income Tax Expense (Benefit)	58.6	45.8
Net Income	253.5	153.0
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Unrealized Gain on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Gain (Loss)	(8.5)	68.3
Credit Losses on Fixed Maturity Securities	(4.1)	(8.3)
Loss on Benefits and Change in Reserves for Future Benefits	0.0	133.1
Income Before Income Tax	(12.6)	(73.1)
Income Tax Expense (Benefit)	(2.6)	(15.4)
Net Income	(10.0)	(57.7)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Gain on Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax	13.7	17.6
Income Tax Expense (Benefit)	2.9	3.7
Net Income	10.8	13.9
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Gain on Hedges | Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Gain (Loss)	0.0	1.8
Net Investment Income	13.4	15.3
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Gain on Hedges | Foreign Exchange Contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Income	0.3	0.5
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses	(4.0)	(5.6)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Prior Service Credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses	0.1	0.1
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Unrecognized Pension and Postretirement Benefit Costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax	(3.9)	(5.5)
Income Tax Expense (Benefit)	(0.8)	(1.2)
Net Income	$ (3.1)	$ (4.3)