Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	$ 1,126	$ (1,643)	$ 4,474	$ (3,069)
Net change, Tax effect	(440)	356	(1,167)	675
Total other comprehensive income/(loss), after–tax	686	(1,287)	3,307	(2,394)
Accumulated other comprehensive income/(loss)
Unrealized gains/(losses) on investment securities:
Total other comprehensive income/(loss), after–tax	686	(1,287)	3,307	(2,394)
Accumulated other comprehensive income/(loss) \| Other income
Unrealized gains/(losses) on investment securities:
Net pre-tax gain (loss) reclassified related to liquidation of legal entity			6
Accumulated other comprehensive income/(loss) \| Other expense
Unrealized gains/(losses) on investment securities:
Net pre-tax gain (loss) reclassified related to liquidation of legal entity			1	(174)
Unrealized gains/(losses) on investment securities
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	708	(1,117)	4,074	(3,351)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	(169)	262	(985)	787
Net unrealized gains/(losses) arising during the period/Translation, After-tax	539	(855)	3,089	(2,564)
Reclassification, Pre-tax	(78)	46	(135)	371
Reclassification, Tax effect	18	(10)	32	(87)
Reclassifications, After-tax	(60)	36	(103)	284
Net change, Pre-tax	630	(1,071)	3,939	(2,980)
Net change, Tax effect	(151)	252	(953)	700
Total other comprehensive income/(loss), after–tax	479	(819)	2,986	(2,280)
Net pre-tax gain (loss) reclassified related to liquidation of legal entity			5
Unrealized gains/(losses) on investment securities \| Other income
Unrealized gains/(losses) on investment securities:
Net pre-tax gain (loss) reclassified related to liquidation of legal entity			5
Unrealized gains/(losses) on investment securities \| Other expense
Unrealized gains/(losses) on investment securities:
Net pre-tax gain (loss) reclassified related to liquidation of legal entity				(23)
Translation adjustments
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(861)	(314)	(697)	(981)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	40	45	76	188
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(821)	(269)	(621)	(793)
Reclassification, Pre-tax	866	311	700	1,149
Reclassification, Tax effect	(210)	(73)	(169)	(272)
Reclassifications, After-tax	656	238	531	877
Net change, Pre-tax	5	(3)	3	168
Net change, Tax effect	(170)	(28)	(93)	(84)
Total other comprehensive income/(loss), after–tax	(165)	(31)	(90)	84
Net pre-tax gain (loss) reclassified related to liquidation of legal entity			2
Translation adjustments \| Other expense
Unrealized gains/(losses) on investment securities:
Net pre-tax gain (loss) reclassified related to liquidation of legal entity				(151)
Fair value hedges, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	(1)	45	114	(96)
Net change, Tax effect	0	(11)	(27)	22
Total other comprehensive income/(loss), after–tax	(1)	34	87	(74)
Cash flow hedges
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	222	(122)	464	(365)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	(55)	27	(112)	85
Net unrealized gains/(losses) arising during the period/Translation, After-tax	167	(95)	352	(280)
Reclassification, Pre-tax	37	9	102	(62)
Reclassification, Tax effect	(9)	(2)	(24)	15
Reclassifications, After-tax	28	7	78	(47)
Net change, Pre-tax	259	(113)	566	(427)
Net change, Tax effect	(64)	25	(136)	100
Total other comprehensive income/(loss), after–tax	195	(88)	430	(327)
Defined benefit pension and OPEB plans
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	60	26	148	103
Net change, Tax effect	(14)	(7)	(25)	(25)
Total other comprehensive income/(loss), after–tax	46	19	123	78
Net gain/(loss)/Amortization of net loss
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	0	0	2	25
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	0	0	(2)	(6)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	0	0	0	19
Reclassification, Pre-tax	42	26	125	78
Reclassification, Tax effect	(10)	(6)	(26)	(18)
Reclassifications, After-tax	32	20	99	60
Amortization of prior service cost/(credit)
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax	0	(7)	2	(19)
Reclassification, Tax effect	0	2	(1)	5
Reclassifications, After-tax	0	(5)	1	(14)
Settlement (gain)/loss
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax			0	0
Reclassification, Tax effect			0	0
Reclassifications, After-tax			0	0
Foreign exchange and other
Unrealized gains/(losses) on investment securities:
Reclassification, Pre-tax	18	7	19	19
Reclassification, Tax effect	(4)	(3)	4	(6)
Reclassifications, After-tax	14	4	23	13
DVA on fair value option elected liabilities, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	173	(527)	(296)	163
Net change, Tax effect	(41)	125	67	(38)
Total other comprehensive income/(loss), after–tax	$ 132	$ (402)	$ (229)	$ 125

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