Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss		$ (17.7)	$ (10.4)	$ (224.5)	$ (11.6)
Impairment Loss	[1]	(8.5)	(1.2)	(160.9)	(1.2)
credit losses		10.6	2.9	11.6	2.9
Net Investment Income		560.7	545.1	1,073.9	1,058.6
Other Expenses		323.5	300.7	642.1	591.8
Income Tax Expense (Benefit)		81.4	106.0	135.9	206.5
Net Income		335.6	389.5	524.7	784.7
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Unrealized Loss on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Net Investment Loss		(13.5)	(5.4)	(58.2)	(21.2)
Impairment Loss		(8.5)	(1.2)	(160.9)	(1.2)
credit losses		(10.6)	(2.9)	(11.6)	(2.9)
Income Before Income Tax		(32.6)	(9.5)	(230.7)	(25.3)
Income Tax Expense (Benefit)		(6.7)	(1.9)	(48.4)	(5.3)
Net Income		(25.9)	(7.6)	(182.3)	(20.0)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax		1.9	4.2	4.4	9.8
Income Tax Expense (Benefit)		0.4	0.8	0.9	2.0
Net Income		(1.5)	(3.4)	(3.5)	(7.8)
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		(0.4)	0.0	0.0	0.0
Net Investment Income		2.5	4.6	4.7	10.4
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		(0.2)	(0.4)	(0.3)	(0.5)
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		4.1	3.9	8.2	8.2
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Prior Service Credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses		0.0	0.0	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		(4.1)	(3.9)	(8.1)	(8.1)
Income Tax Expense (Benefit)		(0.9)	(0.7)	(1.7)	(1.7)
Net Income		$ (3.2)	$ (3.2)	$ (6.4)	$ (6.4)

[1] 2During the three and six months ended June 30, 2025, we recognized impairment losses of $8.5 million and $160.9 million, respectively, based on the intent to dispose of fixed maturity securities related to an anticipated reinsurance transaction.