Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Gain (Loss) on Investments		$ (5.2)	$ (17.7)	$ (10.2)	$ (224.5)
Impairment Loss	[1]	(3.0)	(8.5)	(11.1)	(160.9)
credit losses		0.0	10.6	(5.9)	11.6
Net Investment Income		478.4	560.7	961.8	1,073.9
Other Expenses		366.7	323.5	724.5	642.1
Income Tax Expense (Benefit)		72.6	81.4	143.3	135.9
Net Income		256.9	335.6	488.9	524.7
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		(7.5)	(13.5)	(8.0)	(58.2)
Impairment Loss		(3.0)	(8.5)	(11.1)	(160.9)
credit losses		0.0	(10.6)	5.9	(11.6)
Income Before Income Tax		(10.5)	(32.6)	(13.2)	(230.7)
Income Tax Expense (Benefit)		(2.2)	(6.7)	(2.8)	(48.4)
Net Income		(8.3)	(25.9)	(10.4)	(182.3)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax		1.5	1.9	3.2	4.4
Income Tax Expense (Benefit)		0.3	0.4	0.7	0.9
Net Income		(1.2)	(1.5)	(2.5)	(3.5)
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		0.0	(0.4)	0.0	0.0
Net Investment Income		0.6	2.5	1.4	4.7
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Net Loss on Derivatives | Foreign Exchange Contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Gain (Loss) on Investments		0.9	(0.2)	1.8	(0.3)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Amortization of Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses		2.5	4.1	5.2	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		(2.5)	(4.1)	(5.1)	(8.1)
Income Tax Expense (Benefit)		(0.6)	(0.9)	(1.1)	(1.7)
Net Income		$ (1.9)	$ (3.2)	$ (4.0)	$ (6.4)

[1] During 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 with a fair value of $1,250.9 million related to the 2025 Fortitude Re reinsurance transaction.