Claim and Claim Adjustment Expense Reserves, Reconciliation of Claim and Claim Adjustment Expense Reserves (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance		$ 54	$ 301	$ 179	$ 376
Liability for Unpaid Claim and Claim Adjustment Expenses [Roll Forward]
Gross reserves, beginning of year				22,706	21,720
Ceded reserves, beginning of year				4,005	3,835
Net reserves, beginning of year				18,701	17,885
Reduction of net reserves due to the excess workers' compensation loss portfolio transfer				(632)
Net incurred claim and claim adjustment expenses [Abstract]
Provision for insured events of current year				2,930	2,899
Increase (decrease) in provision for insured events of prior years				(78)	19
Amortization of discount				95	98
Total net incurred	[1]			2,947	3,016
Net payments attributable to [Abstract]
Current year events				(317)	(256)
Prior year events				(1,949)	(2,342)
Total net payments				(2,266)	(2,598)
Foreign currency translation adjustment and other				(5)	(35)
Net reserves, end of period		18,745	18,268	18,745	18,268
Ceded reserves, end of period		4,735	4,002	4,735	4,002
Gross reserves, end of period		$ 23,480	22,270	$ 23,480	22,270
COVID-19 Pandemic [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance			182		195
Civil Unrest [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance			61		61
Severe Weather-Related Events [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance			$ 58		$ 120

[1] Total net incurred above does not agree to Insurance claims and policyholders’ benefits as reflected on the Consolidated Condensed Statements of Operations due to amounts related to retroactive reinsurance deferred gain accounting, the loss on the excess workers’ compensation loss portfolio transfer, uncollectible reinsurance and benefit expenses related to future policy benefits, which are not reflected in the table above.