Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for loan losses
Beginning balance	$ 13,123	$ 13,445	$ 13,604
Gross charge-offs/Write-offs of PCI loans	6,836	6,810	6,349
Gross recoveries collected	(1,577)	(1,181)	(1,493)
Net charge-offs	5,259	5,629	4,856
Provision for loan losses	16,291	5,449	4,885
Other	1	9	(1)
Ending balance	28,328	13,123	13,445
Allowance for lending-related commitments
Beginning balance	1,191	1,055	1,068
Provision for lending-related commitments	1,121	136	(14)
Other	(1)	0	1
Ending balance	2,409	1,191	1,055
Total allowance for credit losses				$ 30,737		$ 14,314	$ 14,500
Allowance for loan losses by impairment methodology
Asset-specific				1,308		847	933
Portfolio-based				27,020		11,289	10,724
PCI						987	1,788
Total allowance for loan losses	28,328	13,445	13,445	28,328		13,123	13,445
Loans by impairment methodology
Asset-specific				21,629		8,536	9,443
Portfolio-based				938,877		916,702	935,935
PCI						20,363	24,037
Total retained loans				960,506		945,601	969,415
Allowance for lending-related commitments by impairment methodology
Asset-specific				114		102	99
Portfolio-based				2,295		1,089	956
Total allowance for lending-related commitments	1,191	1,055	1,055	2,409		1,191	1,055
Lending-related commitments by impairment methodology
Asset-specific				577		474	469
Portfolio-based				464,654		423,384	401,498
Total lending-related commitments				465,231		423,858	401,967
HTM securities, allowance for credit losses				78
HTM securities, provision for credit losses	68
PCI loans
Allowance for loan losses
Gross charge-offs/Write-offs of PCI loans		151	187
Collateral-dependent loans
Allowance for loan losses
Net charge-offs	209	82	45
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell				5,144		2,140	2,282
Cumulative effect of change in accounting principles
Allowance for loan losses
Beginning balance	4,172
Ending balance		4,172
Allowance for lending-related commitments
Beginning balance	98
Ending balance		98
Total allowance for credit losses					$ 4,300
Allowance for loan losses by impairment methodology
Total allowance for loan losses	4,172	4,172				4,172
Allowance for lending-related commitments by impairment methodology
Total allowance for lending-related commitments	98	98				98
Lending-related commitments by impairment methodology
HTM securities, allowance for credit losses					10
Consumer, excluding credit card
Allowance for loan losses
Beginning balance	2,538	3,434	3,892
Gross charge-offs/Write-offs of PCI loans	805	902	977
Gross recoveries collected	(631)	(536)	(827)
Net charge-offs	174	366	150
Provision for loan losses	974	(378)	(121)
Other	1	(1)	0
Ending balance	3,636	2,538	3,434
Allowance for lending-related commitments
Beginning balance	12	12	12
Provision for lending-related commitments	42	0	0
Other	0	0	0
Ending balance	187	12	12
Total allowance for credit losses				3,823		2,550	3,446
Allowance for loan losses by impairment methodology
Asset-specific				(7)		75	143
Portfolio-based				3,643		1,476	1,503
PCI						987	1,788
Total allowance for loan losses	2,538	3,434	3,434	3,636		2,538	3,434
Loans by impairment methodology
Asset-specific				16,648		5,961	6,665
Portfolio-based				285,479		268,675	305,077
PCI						20,363	24,034
Total retained loans				302,127		294,999	335,776
Allowance for lending-related commitments by impairment methodology
Asset-specific				0		0	0
Portfolio-based				187		12	12
Total allowance for lending-related commitments	12	12	12	187		12	12
Lending-related commitments by impairment methodology
Asset-specific				0		0	0
Portfolio-based				37,783		30,417	26,502
Total lending-related commitments				37,783		30,417	26,502
Credit card lending-related commitments not permitted to have an allowance for credit losses				19,500		9,800	8,700
Consumer, excluding credit card | PCI loans
Allowance for loan losses
Gross charge-offs/Write-offs of PCI loans		151	187
Consumer, excluding credit card | Collateral-dependent loans
Allowance for loan losses
Net charge-offs	133	46	16
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell				4,956		2,053	2,076
Consumer, excluding credit card | Cumulative effect of change in accounting principles
Allowance for loan losses
Beginning balance	297
Ending balance		297
Allowance for lending-related commitments
Beginning balance	133
Ending balance		133
Total allowance for credit losses					400
Allowance for loan losses by impairment methodology
Total allowance for loan losses	297	297				297
Allowance for lending-related commitments by impairment methodology
Total allowance for lending-related commitments	133	133				133
Credit card
Allowance for loan losses
Beginning balance	5,683	5,184	4,884
Gross charge-offs/Write-offs of PCI loans	5,077	5,436	5,011
Gross recoveries collected	(791)	(588)	(493)
Net charge-offs	4,286	4,848	4,518
Provision for loan losses	10,886	5,348	4,818
Other	0	(1)	0
Ending balance	17,800	5,683	5,184
Allowance for lending-related commitments
Beginning balance	0	0	0
Provision for lending-related commitments	0	0	0
Other	0	0	0
Ending balance	0	0	0
Total allowance for credit losses				17,800		5,683	5,184
Allowance for loan losses by impairment methodology
Asset-specific				633		477	440
Portfolio-based				17,167		5,206	4,744
PCI						0	0
Total allowance for loan losses	17,800	5,184	4,884	17,800		5,683	5,184
Loans by impairment methodology
Asset-specific				1,375		1,452	1,319
Portfolio-based				142,057		167,472	155,297
PCI						0	0
Total retained loans				143,432		168,924	156,616
Allowance for lending-related commitments by impairment methodology
Asset-specific				0		0	0
Portfolio-based				0		0	0
Total allowance for lending-related commitments	0	0	0	0		0	0
Lending-related commitments by impairment methodology
Asset-specific				0		0	0
Portfolio-based				0		0	0
Total lending-related commitments				0		0	0
Credit card lending-related commitments not permitted to have an allowance for credit losses				658,500		650,700	605,400
Credit card | PCI loans
Allowance for loan losses
Gross charge-offs/Write-offs of PCI loans		0	0
Credit card | Collateral-dependent loans
Allowance for loan losses
Net charge-offs	0	0	0
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell				0		0	0
Credit card | Cumulative effect of change in accounting principles
Allowance for loan losses
Beginning balance	5,517
Ending balance		5,517
Allowance for lending-related commitments
Beginning balance	0
Ending balance		0
Allowance for loan losses by impairment methodology
Total allowance for loan losses	5,517	5,517				5,517
Allowance for lending-related commitments by impairment methodology
Total allowance for lending-related commitments	0	0				0
Wholesale
Allowance for loan losses
Beginning balance	4,902	4,827	4,828
Gross charge-offs/Write-offs of PCI loans	954	472	361
Gross recoveries collected	(155)	(57)	(173)
Net charge-offs	799	415	188
Provision for loan losses	4,431	479	188
Other	0	11	(1)
Ending balance	6,892	4,902	4,827
Allowance for lending-related commitments
Beginning balance	1,179	1,043	1,056
Provision for lending-related commitments	1,079	136	(14)
Other	(1)	0	1
Ending balance	2,222	1,179	1,043
Total allowance for credit losses				9,114		6,081	5,870
Allowance for loan losses by impairment methodology
Asset-specific				682		295	350
Portfolio-based				6,210		4,607	4,477
PCI						0	0
Total allowance for loan losses	6,892	4,827	4,828	6,892		4,902	4,827
Loans by impairment methodology
Asset-specific				3,606		1,123	1,459
Portfolio-based				511,341		480,555	475,561
PCI						0	3
Total retained loans				514,947		481,678	477,023
Allowance for lending-related commitments by impairment methodology
Asset-specific				114		102	99
Portfolio-based				2,108		1,077	944
Total allowance for lending-related commitments	1,179	1,179	1,056	2,222		1,179	1,043
Lending-related commitments by impairment methodology
Asset-specific				577		474	469
Portfolio-based				426,871		392,967	374,996
Total lending-related commitments				427,448		393,441	375,465
Credit card lending-related commitments not permitted to have an allowance for credit losses				22,400		24,100	24,800
Wholesale | PCI loans
Allowance for loan losses
Gross charge-offs/Write-offs of PCI loans		0	0
Wholesale | Collateral-dependent loans
Allowance for loan losses
Net charge-offs	76	36	$ 29
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell				$ 188		87	$ 206
Wholesale | Cumulative effect of change in accounting principles
Allowance for loan losses
Beginning balance	(1,642)
Ending balance		(1,642)
Allowance for lending-related commitments
Beginning balance	(35)
Ending balance		(35)
Total allowance for credit losses					$ (1,600)
Allowance for loan losses by impairment methodology
Total allowance for loan losses	(1,642)	(1,642)				(1,642)
Allowance for lending-related commitments by impairment methodology
Total allowance for lending-related commitments	$ (35)	$ (35)				$ (35)