Accumulated Other Comprehensive Income/(Loss) - Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			$ 279,354
Net change	$ 1,529	$ 1,371	(5,416)	$ 7,220
Ending balance	286,386	264,466	286,386	264,466
Accumulated other comprehensive income/(loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,041	7,418	7,986	1,569
Net change	1,529	1,371	(5,416)	7,220
Ending balance	2,570	8,789	2,570	8,789
Unrealized gains/(losses) on investment securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	3,841	5,176	8,180	4,057
Net change	674	2,744	(3,665)	3,863
Ending balance	4,515	7,920	4,515	7,920
After-tax unamortized unrealized gains related to transfer of AFS securities to HTM			3,000	703
Translation adjustments, net of hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(723)	(1,037)	(473)	(707)
Net change	64	142	(186)	(188)
Ending balance	(659)	(895)	(659)	(895)
Fair value hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(140)	(43)	(112)	(131)
Net change	(23)	16	(51)	104
Ending balance	(163)	(27)	(163)	(27)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	134	2,528	2,383	63
Net change	591	234	(1,658)	2,699
Ending balance	725	2,762	725	2,762
Defined benefit pension and OPEB plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,064)	(1,311)	(1,132)	(1,344)
Net change	9	(7)	77	26
Ending balance	(1,055)	(1,318)	(1,055)	(1,318)
DVA on fair value option elected liabilities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,007)	2,105	(860)	(369)
Net change	214	(1,758)	67	716
Ending balance	$ (793)	$ 347	$ (793)	$ 347