Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Gain (Loss) on Investments	$ (853.0)	$ 128.0	$ (863.2)	$ (96.5)
Impairment Loss	(760.9)	0.0	(772.0)	(160.9)
credit losses	0.0	0.8	(5.9)	12.4
Net Investment Income	522.4	476.8	1,484.2	1,550.7
Other Expenses	361.8	360.0	1,086.3	1,002.1
Income Tax Expense (Benefit)	(129.7)	14.8	13.6	150.7
Net Income	(419.7)	39.7	69.2	564.4
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Unrealized Loss on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Gain (Loss) on Investments	(21.2)	127.7	(29.2)	69.5
Impairment Loss	(750.9)	0.0	(762.0)	(160.9)
credit losses	0.0	(0.8)	5.9	(12.4)
Income (Loss) Before Income Tax	(772.1)	126.9	(785.3)	(103.8)
Income Tax Expense (Benefit)	(162.1)	26.6	(164.9)	(21.8)
Net Income	(610.0)	100.3	(620.4)	(82.0)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income (Loss) Before Income Tax	(10.6)	0.1	(7.4)	4.5
Income Tax Expense (Benefit)	(2.3)	0.0	(1.6)	0.9
Net Income	8.3	(0.1)	5.8	(3.6)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives | Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Gain (Loss) on Investments	(10.0)	(0.9)	(10.0)	(0.9)
Net Investment Income	0.4	1.1	1.8	5.8
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives | Receive Fixed/Pay Fixed
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Gain (Loss) on Investments	(1.0)	(0.1)	0.8	(0.4)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses	2.7	4.2	7.9	12.4
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	0.2	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 (Loss) Before Income Tax	(2.6)	(4.1)	(7.7)	(12.2)
Income Tax Expense (Benefit)	(0.5)	(0.9)	(1.6)	(2.6)
Net Income	$ (2.1)	$ (3.2)	$ (6.1)	$ (9.6)