Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($)		3 Months Ended	12 Months Ended			13 Months Ended
	Feb. 05, 2021	Mar. 31, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Feb. 05, 2021	Dec. 31, 2012	Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group			$ 48,000,000	$ 48,000,000	$ (32,000,000)
Funds held under reinsurance agreements, liability	$ 690,000,000		3,400,000,000	3,600,000,000		$ 690,000,000
Retroactive reinsurance agreement, maximum	1,000,000,000					1,000,000,000
Reinsurance premiums paid	$ 697,000,000					$ 64,000,000
Reinsurance, loss on uncollectible accounts in period, amount		$ 12,000,000
Securities held as collateral, at fair value			298,000,000
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group			79,000,000	71,000,000	64,000,000
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
Net A&EP adverse development before consideration of LPT			103,000,000	86,000,000	92,000,000
Provision for uncollectible third-party reinsurance, released			0	5,000,000	$ 5,000,000
Cumulative amounts ceded under AEP Loss Portfolio Transfer			3,700,000,000	3,600,000,000
Deferred reinsurance benefit yet to be recognized			425,000,000	$ 417,000,000
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer			2,300,000,000
Excess Workers' Compensation LPT
Liability for Claims and Claims Adjustment Expense [Line Items]
Funds held under reinsurance agreements, liability			$ 690,000,000