Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Unusual or Infrequent Item, or Both, Net of Insurance Proceeds	$ 52	$ 19
Retroactive reinsurance benefit recognized	8	$ 12
Cumulative amounts ceded under AEP Loss Portfolio Transfer	3,500		$ 3,500
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	417		$ 425
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer	$ 2,500