Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss		$ 128.0	$ (12.9)	$ (96.5)	$ (24.5)
Impairment Loss	[1]	0.0	(1.3)	(160.9)	(2.5)
credit losses		0.8	0.2	12.4	3.1
Net Investment Income		476.8	527.8	1,550.7	1,586.4
Other Expenses		360.0	311.5	1,002.1	903.3
Income Tax Expense (Benefit)		14.8	168.9	150.7	375.4
Net Income		39.7	645.7	564.4	1,430.4
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Unrealized Loss on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss		127.7	(7.4)	69.5	(28.6)
Impairment Loss		0.0	(1.3)	(160.9)	(2.5)
credit losses		(0.8)	(0.2)	(12.4)	(3.1)
Income Before Income Tax		126.9	(8.9)	(103.8)	(34.2)
Income Tax Expense (Benefit)		26.6	(2.1)	(21.8)	(7.4)
Net Income		100.3	(6.8)	(82.0)	(26.8)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax		0.1	4.0	4.5	13.8
Income Tax Expense (Benefit)		0.0	0.9	0.9	2.9
Net Income		(0.1)	(3.1)	(3.6)	(10.9)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives | Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss		(0.9)	0.0	(0.9)	0.0
Net Investment Income		1.1	3.4	5.8	13.8
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives | Foreign Exchange Contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss		(0.1)	0.6	(0.4)	0.1
Net Investment Income		0.0	0.0	0.0	(0.1)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses		4.2	4.2	12.4	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 Before Income Tax		(4.1)	(4.1)	(12.2)	(12.2)
Income Tax Expense (Benefit)		(0.9)	(0.9)	(2.6)	(2.6)
Net Income		$ (3.2)	$ (3.2)	$ (9.6)	$ (9.6)

[1] 1Our investment gains and losses on fixed maturity securities for the third quarter and first nine months of 2025 were driven primarily by the Closed Block long-term care and Unum US individual disability reinsurance transaction (Fortitude Re reinsurance transaction) which resulted in a net gain of $137.6 million in the third quarter of 2025 and a net loss of $46.8 million in the first nine months of 2025. In addition, we realized a $19.1 million loss on sales of fixed maturity securities relating to funding of a dividend from one of our subsidiaries in the first nine months of 2025