Basis of Presentation - Financial Instruments - Credit Losses, Adoption Impacts (Details) - USD ($) $ in Millions	Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		$ 30,737	$ 14,314	$ 14,500
Allowance for credit losses reclassified		28,328	13,123	13,445	$ 13,604
CECL adoption impact
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	$ 4,300
Balance sheet reclassification	(800)
Total pre-tax impact	3,500
Tax effect	(800)
Decrease to retained earnings	2,700
Allowance for credit losses reclassified			4,172
Adjusted balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	18,600
Consumer, excluding credit card
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		3,823	2,550	3,446
Allowance for credit losses reclassified		3,636	2,538	3,434	3,892
Consumer, excluding credit card | Revisions
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses reclassified			600
Consumer, excluding credit card | CECL adoption impact
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	400
Allowance for credit losses reclassified			297
Consumer, excluding credit card | CECL adoption impact | Revisions
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses reclassified	(200)
Consumer, excluding credit card | Adjusted balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	3,000
Credit card
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses			5,700
Credit card | CECL adoption impact
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	5,500
Credit card | Adjusted balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	11,200
Wholesale
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		9,114	6,081	5,870
Allowance for credit losses reclassified		$ 6,892	4,902	$ 4,827	$ 4,828
Wholesale | CECL adoption impact
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	(1,600)
Allowance for credit losses reclassified			$ (1,642)
Wholesale | Adjusted balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	$ 4,400