Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss	$ (31.0)	$ (4.4)	$ (30.0)	$ (22.3)
Net Investment Income	526.0	511.6	1,565.9	1,597.8
Other Expenses	(271.8)	(243.9)	(818.6)	(734.4)
Income Tax Expense (Benefit)	59.7	131.3	258.2	258.5
Net Income	202.0	510.3	953.2	1,118.0
credit losses	0.0	(0.5)	0.0	(4.6)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Unrealized Gain (Loss) on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss	(37.0)	(13.4)	(47.0)	(25.6)
Income Before Income Tax	(37.0)	(13.9)	(47.0)	(30.2)
Income Tax Expense (Benefit)	(7.7)	(2.8)	(9.8)	(6.3)
Net Income	(29.3)	(11.1)	(37.2)	(23.9)
credit losses	0.0	(0.5)	0.0	(4.6)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Gain (Loss) on Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax	8.2	12.6	27.5	39.5
Income Tax Expense (Benefit)	1.7	2.7	5.8	8.3
Net Income	(6.5)	(9.9)	(21.7)	(31.2)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Gain (Loss) on Hedges | Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Income	8.3	14.1	27.6	40.5
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Gain (Loss) on Hedges | Foreign Exchange Contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss	0.0	0.0	0.1	0.0
Net Investment Income	(0.1)	(1.5)	(0.2)	(1.0)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses	(1.8)	(4.0)	(5.4)	(11.8)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Prior Service Credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses	0.0	0.1	0.1	0.2
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	(1.8)	(3.9)	(5.3)	(11.6)
Income Tax Expense (Benefit)	(0.4)	(0.8)	(1.1)	(2.4)
Net Income	$ (1.4)	$ (3.1)	$ (4.2)	$ (9.2)