Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	$ 1,279	$ (1,387)
Net change, Tax effect	(330)	355
Total other comprehensive income/(loss), after–tax	949	(1,032)
Unrealized gains/(losses) on investment securities
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	1,875	(1,858)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	(451)	437
Net unrealized gains/(losses) arising during the period/Translation, After-tax	1,424	(1,421)
Reclassification, Pre-tax	(13)	245
Reclassification, Tax effect	3	(58)
Reclassifications, After-tax	(10)	187
Net change, Pre-tax	1,862	(1,613)
Net change, Tax effect	(448)	379
Total other comprehensive income/(loss), after–tax	1,414	(1,234)
Translation adjustments
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	41	389
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	(36)	(65)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	5	324
Reclassification, Pre-tax	(38)	(389)
Reclassification, Tax effect	9	92
Reclassifications, After-tax	(29)	(297)
Net change, Pre-tax	3	0
Net change, Tax effect	(27)	27
Total other comprehensive income/(loss), after–tax	(24)	27
Fair value hedges, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	3	(52)
Net change, Tax effect	(1)	12
Total other comprehensive income/(loss), after–tax	2	(40)
Cash flow hedges
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	141	(44)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	(33)	11
Net unrealized gains/(losses) arising during the period/Translation, After-tax	108	(33)
Reclassification, Pre-tax	39	(52)
Reclassification, Tax effect	(9)	12
Reclassifications, After-tax	30	(40)
Net change, Pre-tax	180	(96)
Net change, Tax effect	(42)	23
Total other comprehensive income/(loss), after–tax	138	(73)
Defined benefit pension and OPEB plans
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	38	24
Net change, Tax effect	(2)	(3)
Total other comprehensive income/(loss), after–tax	36	21
Net gain/(loss)/Amortization of net loss
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	3	23
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	(2)	(6)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	1	17
Reclassification, Pre-tax	42	26
Reclassification, Tax effect	(9)	(6)
Reclassifications, After-tax	33	20
Amortization of prior service cost/(credit)
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax	1	(6)
Reclassification, Tax effect	0	1
Reclassifications, After-tax	1	(5)
Foreign exchange and other
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax	(8)	(19)
Reclassification, Tax effect	9	8
Reclassifications, After-tax	1	(11)
DVA on fair value option elected liabilities, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	(807)	350
Net change, Tax effect	190	(83)
Total other comprehensive income/(loss), after–tax	$ (617)	$ 267

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