Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	$ (1,643)	$ 129	$ (3,069)	$ 1,398
Net change, Tax effect	356	(46)	675	(532)
Total other comprehensive income/(loss), after–tax	(1,287)	83	(2,394)	866
Accumulated other comprehensive income/(loss)
Unrealized gains/(losses) on investment securities:
Total other comprehensive income/(loss), after–tax			(2,394)	866
Net pre-tax loss reclassified to other expense related to liquidation of legal entity			174	25
Unrealized gains/(losses) on investment securities
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(1,117)	232	(3,351)	1,294
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	262	(86)	787	(476)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(855)	146	(2,564)	818
Reclassification, Pre-tax	46	1	371	38
Reclassification, Tax effect	(10)	0	(87)	(14)
Reclassifications, After-tax	36	1	284	24
Net change, Pre-tax	(1,071)	233	(2,980)	1,332
Net change, Tax effect	252	(86)	700	(490)
Total other comprehensive income/(loss), after–tax	(819)	147	(2,280)	842
Net pre-tax loss reclassified to other expense related to liquidation of legal entity			23	47
Translation adjustments
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(314)	286	(981)	1,185
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	45	(106)	188	(448)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(269)	180	(793)	737
Reclassification, Pre-tax	311	(286)	1,149	(1,161)
Reclassification, Tax effect	(73)	106	(272)	431
Reclassifications, After-tax	238	(180)	877	(730)
Net change, Pre-tax	(3)	0	168	24
Net change, Tax effect	(28)	0	(84)	(17)
Total other comprehensive income/(loss), after–tax	(31)	0	84	7
Net pre-tax loss reclassified to other expense related to liquidation of legal entity			151	72
Fair value hedges
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	45		(96)
Net change, Tax effect	(11)		22
Total other comprehensive income/(loss), after–tax	34		(74)
Cash flow hedges
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(122)	29	(365)	111
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	27	(11)	85	(42)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(95)	18	(280)	69
Reclassification, Pre-tax	9	10	(62)	160
Reclassification, Tax effect	(2)	(2)	15	(59)
Reclassifications, After-tax	7	8	(47)	101
Net change, Pre-tax	(113)	39	(427)	271
Net change, Tax effect	25	(13)	100	(101)
Total other comprehensive income/(loss), after–tax	(88)	26	(327)	170
Defined benefit pension and OPEB plans
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	26	35	103	54
Net change, Tax effect	(7)	(13)	(25)	(28)
Total other comprehensive income/(loss), after–tax	19	22	78	26
Net gain/(losses)/Amortization of net loss
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	0	0	25	(52)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	0	0	(6)	19
Net unrealized gains/(losses) arising during the period/Translation, After-tax	0	0	19	(33)
Reclassification, Pre-tax	26	63	78	187
Reclassification, Tax effect	(6)	(23)	(18)	(69)
Reclassifications, After-tax	20	40	60	118
Prior service costs/(credits)
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax	(7)	(9)	(19)	(27)
Reclassification, Tax effect	2	3	5	10
Reclassifications, After-tax	(5)	(6)	(14)	(17)
Settlement (gain)/loss
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax			0	(3)
Reclassification, Tax effect			0	1
Reclassifications, After-tax			0	(2)
Foreign exchange and other
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax	7	(19)	19	(51)
Reclassification, Tax effect	(3)	7	(6)	11
Reclassifications, After-tax	4	(12)	13	(40)
DVA on fair value option elected liabilities, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	(527)	(178)	163	(283)
Net change, Tax effect	125	66	(38)	104
Total other comprehensive income/(loss), after–tax	$ (402)	$ (112)	$ 125	$ (179)

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