Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2012	Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items]
Unusual or infrequent item, or both, net of insurance proceeds	$ 19	$ 125
Retroactive reinsurance benefit recognized	12	$ 10
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	$ 2,200
Cumulative amounts ceded under AEP Loss Portfolio Transfer	3,400		$ 3,400
Deferred reinsurance benefit yet to be recognized	417		$ 429
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer	$ 3,100