Accumulated Other Comprehensive Income/(Loss) - Components of Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrealized gains/(losses) on AFS securities:
Net change, Pre-tax	$ (1,761)	$ 1,971	$ (2,451)
Net change, Tax effect	285	(915)	930
Total other comprehensive income/(loss), after–tax	(1,476)	1,056	(1,521)
Accumulated other comprehensive income/(loss)
Unrealized gains/(losses) on AFS securities:
Total other comprehensive income/(loss), after–tax	(1,476)	1,056	(1,521)
Net pre-tax loss reclassified to other expense related to liquidation of legal entity	168	25
Unrealized gains/(losses) on investment securities
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(2,825)	944	(1,628)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	665	(346)	611
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(2,160)	598	(1,017)
Reclassification, Pre-tax	395	66	(141)
Reclassification, Tax effect	(93)	(24)	53
Reclassification, After-tax	302	42	(88)
Net change, Pre-tax	(2,430)	1,010	(1,769)
Net change, Tax effect	572	(370)	664
Total other comprehensive income/(loss), after–tax	(1,858)	640	(1,105)
Net pre-tax loss reclassified to other expense related to liquidation of legal entity	17	50
Translation adjustments
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(1,078)	1,313	(261)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	156	(801)	99
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(922)	512	(162)
Reclassification, Pre-tax	1,236	(1,294)	262
Reclassification, Tax effect	(294)	476	(102)
Reclassification, After-tax	942	(818)	160
Net change, Pre-tax	158	19	1
Net change, Tax effect	(138)	(325)	(3)
Total other comprehensive income/(loss), after–tax	20	(306)	(2)
Net pre-tax loss reclassified to other expense related to liquidation of legal entity	151	75
Fair value hedges, net of change
Unrealized gains/(losses) on AFS securities:
Net change, Pre-tax	(140)
Net change, Tax effect	33
Total other comprehensive income/(loss), after–tax	(107)
Cash flow hedges
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(245)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	58
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(187)
Reclassification, Pre-tax	(18)
Reclassification, Tax effect	4
Reclassification, After-tax	(14)
Net change, Pre-tax	(263)
Net change, Tax effect	62
Total other comprehensive income/(loss), after–tax	(201)
Cash flow hedges
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax		147	(450)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect		(55)	168
Net unrealized gains/(losses) arising during the period/Translation, After-tax		92	(282)
Reclassification, Pre-tax		134	360
Reclassification, Tax effect		(50)	(134)
Reclassification, After-tax		84	226
Net change, Pre-tax		281	(90)
Net change, Tax effect		(105)	34
Total other comprehensive income/(loss), after–tax		176	(56)
Defined benefit pension and OPEB plans
Unrealized gains/(losses) on AFS securities:
Net change, Pre-tax	(450)	964	(64)
Net change, Tax effect	77	(226)	36
Total other comprehensive income/(loss), after–tax	(373)	738	(28)
Prior service credit/(cost)/Amortization of prior services cost/(credit)
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(29)	0	0
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	7	0	0
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(22)	0	0
Reclassification, Pre-tax	(23)	(36)	(36)
Reclassification, Tax effect	6	13	14
Reclassification, After-tax	(17)	(23)	(22)
Net gain/(loss)/Amortization of net loss
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(558)	802	(366)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	102	(160)	145
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(456)	642	(221)
Reclassification, Pre-tax	103	250	257
Reclassification, Tax effect	(24)	(90)	(97)
Reclassification, After-tax	79	160	160
Curtailment (gain)/loss
Unrealized gains/(losses) on AFS securities:
Reclassification, Pre-tax	21	0	0
Reclassification, Tax effect	(5)	0	0
Reclassification, After-tax	16	0	0
Settlement (gain)/loss
Unrealized gains/(losses) on AFS securities:
Reclassification, Pre-tax	2	2	4
Reclassification, Tax effect	0	(1)	(1)
Reclassification, After-tax	2	1	3
Foreign exchange and other
Unrealized gains/(losses) on AFS securities:
Reclassification, Pre-tax	34	(54)	77
Reclassification, Tax effect	(9)	12	(25)
Reclassification, After-tax	25	(42)	52
DVA on fair value option elected liabilities, net change
Unrealized gains/(losses) on AFS securities:
Net change, Pre-tax	1,364	(303)	(529)
Net change, Tax effect	(321)	111	199
Total other comprehensive income/(loss), after–tax	$ 1,043	$ (192)	$ (330)

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