Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Unusual or infrequent item, or both, net of insurance proceeds	$ 41	$ 143	$ 200	$ 313
Pretax (favorable) unfavorable premium development, excluding Life & Group	(1)	17	190	33
Retroactive reinsurance benefit recognized	14	$ 11	39	36
Cumulative amounts ceded under AEP Loss Portfolio Transfer	3,700		3,700		$ 3,700
Hurricane Helene
Liability for Claims and Claims Adjustment Expense [Line Items]
Unusual or infrequent item, or both, net of insurance proceeds				$ 55
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
Aggregate limit under A&EP Loss Portfolio Transfer						4,000
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
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer						2,000
Net reinsurance receivables transferred to NICO under A&EP Loss Portfolio Transfer						215
Total consideration paid to NICO under AEP Loss Portfolio Transfer						$ 2,200
Deferred reinsurance benefit yet to be recognized	386		386		$ 425
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer	$ 2,300		2,300
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group			$ 134