Claim and Claim Adjustment Expense and Future Policy Benefit Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Reserves, beginning of year: [Abstract]
Gross	$ 21,984	$ 22,004
Ceded	4,019	3,934
Net reserves, beginning of year	17,965	18,070
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	3,968	3,866
Increase (decrease) in provision for insured events of prior years	(65)	(173)
Amortization of discount	143	136
Total net incurred	4,046	3,829
Net payments attributable to:
Current year events	(599)	(658)
Prior year events	(3,547)	(3,415)
Total net payments	(4,146)	(4,073)
Foreign currency translation adjustment and other	29	(80)
Net reserves, end of period	17,894	17,746
Ceded reserves, end of period	3,702	3,858
Gross reserves, end of period	$ 21,596	$ 21,604