Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Unrealized gains/(losses) on investment securities:
Total other comprehensive income/(loss), after–tax	$ (1,607)	$ 151	$ (7,023)	$ 7,371
Accumulated other comprehensive income/(loss)
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	(1,874)	26	(8,758)	9,785
Net change, Tax effect	267	125	1,735	(2,414)
Total other comprehensive income/(loss), after–tax	(1,607)	151	(7,023)	7,371
Unrealized gains/(losses) on investment securities
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(826)	1,143	(5,792)	6,494
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	197	(270)	1,391	(1,561)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(629)	873	(4,401)	4,933
Reclassification adjustment for realized (gains)/losses included in net income, Pre-tax	256	(473)	397	(732)
Reclassification adjustment for realized (gains)/losses included in net income, Tax effect	(61)	114	(95)	176
Reclassification adjustment for realized (gains)/losses included in net income, After-tax	195	(359)	302	(556)
Net change, Pre-tax	(570)	670	(5,395)	5,762
Net change, Tax effect	136	(156)	1,296	(1,385)
Total other comprehensive income/(loss), after–tax	(434)	514	(4,099)	4,377
Translation adjustments
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(1,030)	871	(1,950)	(316)
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	63	(86)	92	15
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(967)	785	(1,858)	(301)
Reclassification adjustment for realized (gains)/losses included in net income, Pre-tax	1,028	(868)	1,958	316
Reclassification adjustment for realized (gains)/losses included in net income, Tax effect	(248)	210	(473)	(76)
Reclassification adjustment for realized (gains)/losses included in net income, After-tax	780	(658)	1,485	240
Net change, Pre-tax	(2)	3	8	0
Net change, Tax effect	(185)	124	(381)	(61)
Total other comprehensive income/(loss), after–tax	(187)	127	(373)	(61)
Fair value hedges, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	12	(91)	(56)	45
Net change, Tax effect	(3)	22	14	(10)
Total other comprehensive income/(loss), after–tax	9	(69)	(42)	35
Cash flow hedges
Unrealized gains/(losses) on investment securities:
Net unrealized gains/(losses) arising during the period/Translation, Pre-tax	(267)	134	(1,844)	3,787
Net unrealized gains/(losses) arising during the period/Translation, Tax effect	65	(32)	443	(909)
Net unrealized gains/(losses) arising during the period/Translation, After-tax	(202)	102	(1,401)	2,878
Reclassification adjustment for realized (gains)/losses included in net income, Pre-tax	(326)	(227)	(930)	(328)
Reclassification adjustment for realized (gains)/losses included in net income, Tax effect	78	55	223	79
Reclassification adjustment for realized (gains)/losses included in net income, After-tax	(248)	(172)	(707)	(249)
Net change, Pre-tax	(593)	(93)	(2,774)	3,459
Net change, Tax effect	143	23	666	(830)
Total other comprehensive income/(loss), after–tax	(450)	(70)	(2,108)	2,629
Defined benefit pension and OPEB plans, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	8	(18)	101	23
Net change, Tax effect	(2)	6	(18)	(9)
Total other comprehensive income/(loss), after–tax	6	(12)	83	14
DVA on fair value option elected liabilities, net change
Unrealized gains/(losses) on investment securities:
Net change, Pre-tax	(729)	(445)	(642)	496
Net change, Tax effect	178	106	158	(119)
Total other comprehensive income/(loss), after–tax	$ (551)	$ (339)	$ (484)	$ 377

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