Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($)		12 Months Ended
	Feb. 05, 2021	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2013	Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group		$ 185,000,000	$ 48,000,000	$ 48,000,000
Net A&EP adverse development before consideration of LPT		185,000,000	103,000,000	86,000,000
Funds held under reinsurance agreements, liability	$ 690,000,000	3,800,000,000	3,400,000,000
Retroactive reinsurance agreement, maximum	1,000,000,000
Reinsurance premiums paid	$ 697,000,000
Securities held as collateral, at fair value		247,000,000
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group		134,000,000	79,000,000	$ 71,000,000
Asbestos and Environmental Reserves
Liability for Claims and Claims Adjustment Expense [Line Items]
Net A&EP claim and allocated claim adjustment expense reserves ceded to NICO						$ 1,600,000,000
Aggregate limit under A&EP Loss Portfolio Transfer						4,000,000,000
A&EP claim and allocated claim adjustment expense reserves ceded under existing third party reinsurance contracts transferred to NICO under A&EP Loss Portfolio Transfer						1,200,000,000
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer						2,000,000,000
Net reinsurance receivables transferred to NICO under A&EP Loss Portfolio Transfer						215,000,000
Total consideration paid to NICO under AEP Loss Portfolio Transfer					$ 2,200,000,000	$ 2,200,000,000
Cumulative amounts ceded under AEP Loss Portfolio Transfer		3,900,000,000	3,700,000,000
Deferred reinsurance benefit yet to be recognized		470,000,000	$ 425,000,000
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer		2,400,000,000
Excess Workers' Compensation LPT
Liability for Claims and Claims Adjustment Expense [Line Items]
Funds held under reinsurance agreements, liability		615,000,000
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		$ 75,000,000