Accumulated Other Comprehensive Income/(Loss) - Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 261,330	$ 256,515
Net change	6,417	3,076	$ (1,476)
Ending balance	279,354	261,330	256,515
Accumulated other comprehensive income/(loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,569	(1,507)	(119)
Net change	6,417	3,076	(1,476)
Ending balance	7,986	1,569	(1,507)
Accumulated other comprehensive income/(loss) | Cumulative effect of change in accounting principles
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			88
Unrealized gains/(losses) on investment securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	4,057	1,202	2,164
Net change	4,123	2,855	(1,858)
Ending balance	8,180	4,057	1,202
After-tax unamortized unrealized gains related to transfer of AFS securities to HTM	3,300
Unrealized gains/(losses) on investment securities | Cumulative effect of change in accounting principles
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			896
Translation adjustments, net of hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(707)	(727)	(470)
Net change	234	20	20
Ending balance	(473)	(707)	(727)
Translation adjustments, net of hedges | Cumulative effect of change in accounting principles
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(277)
Fair value hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(131)	(161)	0
Net change	19	30	(107)
Ending balance	(112)	(131)	(161)
Fair value hedges | Cumulative effect of change in accounting principles
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(54)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	63	(109)	76
Net change	2,320	172	(201)
Ending balance	2,383	63	(109)
Cash flow hedges | Cumulative effect of change in accounting principles
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			16
Defined benefit pension and OPEB plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,344)	(2,308)	(1,521)
Net change	212	964	(373)
Ending balance	(1,132)	(1,344)	(2,308)
Defined benefit pension and OPEB plans | Cumulative effect of change in accounting principles
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(414)
DVA on fair value option elected liabilities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(369)	596	(368)
Net change	(491)	(965)	1,043
Ending balance	$ (860)	$ (369)	596
DVA on fair value option elected liabilities | Cumulative effect of change in accounting principles
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			$ (79)