Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Allowance for Credit Losses and Reserve for Unfunded Lending Commitments Activity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2019
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance			$ 15,564
Provision (benefit) for credit losses	$ (342)	$ 331	(2,325)	$ 10,000
Balance at the end of the period	11,573		11,573
Financing Receivable Allowance for credit loss Translation Adjustments and Purchase Credit Deteriorated Loans	6		6
Other
Allowance for Credit Losses [Roll Forward]
Provision (benefit) for credit losses	0	(2)	(2)	2
Allowance for credit losses
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	12,346	16,832	15,564	7,208
Charge-offs	(1,019)	(1,679)	(3,608)	(6,267)
Recoveries	593	606	1,901	1,898
Net charge-offs	(426)	(1,073)	(1,707)	(4,369)
Provision (benefit) for credit losses	(344)	356	(2,294)	9,975
Allowance build (release) for credit losses	(770)	(717)	(4,001)	5,606
Other changes	(3)	14	10	8
Balance at the end of the period	11,573	16,129	11,573	16,129
Allowance for credit losses | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					$ 2,845
Allowance for credit losses | Finance charge and fee reserve reclassification
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					462
Allowance for credit losses | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				10,515
Reserve for unfunded lending commitments
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	164	218	195	135
Provision (benefit) for credit losses	2	(23)	(29)	23
Balance at the end of the period	166	195	166	195
Reserve for unfunded lending commitments | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					37
Reserve for unfunded lending commitments | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				172
Combined allowance and reserve
Allowance for Credit Losses [Roll Forward]
Balance at the end of the period	11,739	16,324	11,739	16,324
Credit Card | Allowance for credit losses
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	8,873	12,091	11,191	5,395
Charge-offs	(735)	(1,296)	(2,695)	(4,757)
Recoveries	369	353	1,125	1,167
Net charge-offs	(366)	(943)	(1,570)	(3,590)
Provision (benefit) for credit losses	(198)	450	(1,325)	7,096
Allowance build (release) for credit losses	(564)	(493)	(2,895)	3,506
Other changes	(3)	14	10	8
Balance at the end of the period	8,306	11,612	8,306	11,612
Credit Card | Allowance for credit losses | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					2,241
Credit Card | Allowance for credit losses | Finance charge and fee reserve reclassification
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					462
Credit Card | Allowance for credit losses | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				8,098
Credit Card | Reserve for unfunded lending commitments
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	0	0	0	0
Provision (benefit) for credit losses	0	0	0	0
Balance at the end of the period	0	0	0	0
Credit Card | Reserve for unfunded lending commitments | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					0
Credit Card | Reserve for unfunded lending commitments | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				0
Credit Card | Combined allowance and reserve
Allowance for Credit Losses [Roll Forward]
Balance at the end of the period	8,306	11,612	8,306	11,612
Consumer Banking | Allowance for credit losses
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	2,203	2,838	2,715	1,038
Charge-offs	(264)	(295)	(866)	(1,207)
Recoveries	213	247	735	721
Net charge-offs	(51)	(48)	(131)	(486)
Provision (benefit) for credit losses	(91)	(43)	(523)	1,693
Allowance build (release) for credit losses	(142)	(91)	(654)	1,207
Other changes	0	0	0	0
Balance at the end of the period	2,061	2,747	2,061	2,747
Consumer Banking | Allowance for credit losses | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					502
Consumer Banking | Allowance for credit losses | Finance charge and fee reserve reclassification
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					0
Consumer Banking | Allowance for credit losses | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				1,540
Consumer Banking | Reserve for unfunded lending commitments
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	0	0	0	5
Provision (benefit) for credit losses	0	0	0	0
Balance at the end of the period	0	0	0	0
Consumer Banking | Reserve for unfunded lending commitments | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					(5)
Consumer Banking | Reserve for unfunded lending commitments | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				0
Consumer Banking | Combined allowance and reserve
Allowance for Credit Losses [Roll Forward]
Balance at the end of the period	2,061	2,747	2,061	2,747
Commercial Banking | Allowance for credit losses
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	1,270	1,903	1,658	775
Charge-offs	(20)	(88)	(47)	(303)
Recoveries	11	6	41	10
Net charge-offs	(9)	(82)	(6)	(293)
Provision (benefit) for credit losses	(55)	(51)	(446)	1,186
Allowance build (release) for credit losses	(64)	(133)	(452)	893
Other changes	0	0	0	0
Balance at the end of the period	1,206	1,770	1,206	1,770
Commercial Banking | Allowance for credit losses | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					102
Commercial Banking | Allowance for credit losses | Finance charge and fee reserve reclassification
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					0
Commercial Banking | Allowance for credit losses | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				877
Commercial Banking | Reserve for unfunded lending commitments
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance	164	218	195	130
Provision (benefit) for credit losses	2	(23)	(29)	23
Balance at the end of the period	166	195	166	195
Commercial Banking | Reserve for unfunded lending commitments | Cumulative effects from adoption of new accounting standards
Allowance for Credit Losses [Roll Forward]
Allowance for credit loss					$ 42
Commercial Banking | Reserve for unfunded lending commitments | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Beginning Balance				172
Commercial Banking | Combined allowance and reserve
Allowance for Credit Losses [Roll Forward]
Balance at the end of the period	$ 1,372	$ 1,965	$ 1,372	$ 1,965