Claim and Claim Adjustment Expense Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserves, beginning of year: [Abstract]
Gross		$ 22,343	$ 22,663	$ 23,271
Ceded		4,094	4,087	4,344
Net reserves, beginning of year		18,249	18,576	18,927
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year		5,201	5,025	4,934
Decrease in provision for insured events of prior years		(381)	(342)	(255)
Amortization of discount		179	175	166
Total net incurred	[1]	4,999	4,858	4,845
Net payments attributable to:
Current year events		(975)	(967)	(856)
Prior year events		(4,366)	(4,167)	(4,089)
Total net payments		(5,341)	(5,134)	(4,945)
Foreign currency translation adjustment and other		163	(51)	(251)
Net reserves, end of year		18,070	18,249	18,576
Ceded reserves, end of year		3,934	4,094	4,087
Gross reserves, end of year		$ 22,004	$ 22,343	$ 22,663

[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 loss deductible receivables, and benefit expenses related to future policy benefits, which are not reflected in the table above.