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Income Taxes (Provision for (Benefit from) Income Taxes) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
U.S. federal									$ 686	$ 476	$ 330
U.S. state and local									207	125	221
Current income tax expense (benefit)									1,901	1,414	1,148
Deferred:
U.S. federal									330	2,656	1,336
U.S. state and local									56	84	74
Deferred income tax expense (benefit)									449	2,754	1,578
Provision for income taxes from continuing operations	$ 300	$ 696	$ 640	$ 714	$ 1,810	$ 697	$ 846	$ 815	2,350	4,168	2,726
Provision for (benefit from) income taxes from discontinued operations									(1)	(7)	1
U.K.
Current:
Non-U.S.									328	401	196
Deferred:
Non-U.S.									54	18	56
Japan
Current:
Non-U.S.									268	56	28
Deferred:
Non-U.S.									(10)	(17)	127
Hong Kong
Current:
Non-U.S.									94	48	14
Deferred:
Non-U.S.									(3)	(2)	31
Other
Current:
Non-U.S.									318	308	359
Deferred:
Non-U.S.									22	15	(46)
Brazil
Tax provisions related to selected other non-U.S. jurisdictions
Foreign tax provisions									71	82	125
Canada
Tax provisions related to selected other non-U.S. jurisdictions
Foreign tax provisions										36
France
Tax provisions related to selected other non-U.S. jurisdictions
Foreign tax provisions											38
India
Tax provisions related to selected other non-U.S. jurisdictions
Foreign tax provisions									39	$ 49	$ 46
Spain
Tax provisions related to selected other non-U.S. jurisdictions
Foreign tax provisions									$ 67