Claim and Claim Adjustment Expense Reserves, Reconciliation of Claim and Claim Adjustment Expense Reserves (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance		$ 125	$ 75
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		1,474	1,355
Increase (decrease) in provision for insured events of prior years		(54)	(8)
Amortization of discount		50	51
Total net incurred	[1]	1,470	1,398
Net payments attributable to [Abstract]
Current year events		(85)	(72)
Prior year events		(1,067)	(1,218)
Total net payments		(1,152)	(1,290)
Foreign currency translation adjustment and other		(32)	(88)
Net reserves, end of period		18,355	17,905
Ceded reserves, end of period		4,701	3,967
Gross reserves, end of period		$ 23,056	21,872
COVID-19 Pandemic [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance			13
U.S. Weather Related Events [Member]
Claim and Claim Adjustment Expense Reserves [Abstract]
Catastrophe losses, net of reinsurance			$ 62

[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.