Claim and Claim Adjustment Expense Reserves, Reconciliation of Claim and Claim Adjustment Expense Reserves (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance		$ 178	$ 160	$ 357	$ 536
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				4,474	4,425
Increase (decrease) in provision for insured events of prior years				(130)	(68)
Amortization of discount				137	143
Total net incurred	[1]			4,481	4,500
Net payments attributable to [Abstract]
Current year events				(629)	(556)
Prior year events				(2,874)	(3,285)
Total net payments				(3,503)	(3,841)
Foreign currency translation adjustment and other				(51)	39
Net reserves, end of period		18,996	18,583	18,996	18,583
Ceded reserves, end of period		4,836	3,951	4,836	3,951
Gross reserves, end of period		23,832	$ 22,534	$ 23,832	22,534
Hurricane Ida [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance		$ 114
Severe Weather-Related Events [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance					273
COVID-19 Pandemic [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance					195
Civil Unrest [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance					$ 68

[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.