Accumulated Other Comprehensive Income/(Loss) - Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 279,354
Net change	(6,945)	$ 5,849
Ending balance	280,714	261,262
Accumulated other comprehensive income/(loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	7,986	1,569
Net change	(6,945)	5,849
Ending balance	1,041	7,418
Unrealized gains/(losses) on investment securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	8,180	4,057
Net change	(4,339)	1,119
Ending balance	3,841	5,176
After-tax unamortized unrealized gains related to transfer of AFS securities to HTM	2,900	737
Translation adjustments, net of hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(473)	(707)
Net change	(250)	(330)
Ending balance	(723)	(1,037)
Fair value hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(112)	(131)
Net change	(28)	88
Ending balance	(140)	(43)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	2,383	63
Net change	(2,249)	2,465
Ending balance	134	2,528
Defined benefit pension and OPEB plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,132)	(1,344)
Net change	68	33
Ending balance	(1,064)	(1,311)
DVA on fair value option elected liabilities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(860)	(369)
Net change	(147)	2,474
Ending balance	$ (1,007)	$ 2,105