Accumulated Other Comprehensive Income/(Loss) - Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			$ 279,354
Net change	$ (1,607)	$ 151	(7,023)	$ 7,371
Ending balance	290,041	271,113	290,041	271,113
Accumulated other comprehensive income/(loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	2,570	8,789	7,986	1,569
Net change	(1,607)	151	(7,023)	7,371
Ending balance	963	8,940	963	8,940
Unrealized gains/(losses) on investment securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	4,515	7,920	8,180	4,057
Net change	(434)	514	(4,099)	4,377
Ending balance	4,081	8,434	4,081	8,434
After-tax unamortized unrealized gains related to transfer of AFS securities to HTM			2,700	2,700
Translation adjustments, net of hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(659)	(895)	(473)	(707)
Net change	(187)	127	(373)	(61)
Ending balance	(846)	(768)	(846)	(768)
Fair value hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(163)	(27)	(112)	(131)
Net change	9	(69)	(42)	35
Ending balance	(154)	(96)	(154)	(96)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	725	2,762	2,383	63
Net change	(450)	(70)	(2,108)	2,629
Ending balance	275	2,692	275	2,692
Defined benefit pension and OPEB plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,055)	(1,318)	(1,132)	(1,344)
Net change	6	(12)	83	14
Ending balance	(1,049)	(1,330)	(1,049)	(1,330)
DVA on fair value option elected liabilities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(793)	347	(860)	(369)
Net change	(551)	(339)	(484)	377
Ending balance	$ (1,344)	$ 8	$ (1,344)	$ 8