Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Reconciliation of Claim and Claim Adjustment Expense Reserves (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claim and Claim Adjustment Expenses [Roll Forward]
Gross reserves, beginning of year		$ 21,720		$ 21,984	$ 22,004
Ceded reserves, beginning of year		3,835		4,019	3,934
Net reserves, beginning of year		17,885		17,965	18,070
Net incurred claim and claim adjustment expenses [Abstract]
Provision for insured events of current year		5,793		5,356	5,358
Decrease in provision for insured events of prior years		(119)		(127)	(179)
Amortization of discount		183		184	176
Total net incurred	[1]	5,857		5,413	5,355
Net payments attributable to [Abstract]
Current year events		(948)		(992)	(1,046)
Prior year events		(4,216)		(4,584)	(4,285)
Total net payments		(5,164)		(5,576)	(5,331)
Foreign currency translation adjustment and other		123		83	(129)
Net reserves, end of year		18,701		17,885	17,965
Ceded reserves, end of year		4,005	[2]	3,835	4,019
Gross reserves, end of year		$ 22,706		$ 21,720	$ 21,984

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

[2] Reinsurance receivables presented are gross of the allowance for uncollectible reinsurance and do not include reinsurance receivables related to paid losses.