Loans - Loan Portfolio Composition and Aging Analysis (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Current	$ 255,823	$ 245,060
Total	$ 261,390	$ 251,624
Current, percentage of total loans	97.87%	97.39%
Percentage of total loans	100.00%	100.00%
Unamortized premiums and discounts, deferred fees and costs	$ 1,400	$ 1,100
Credit Card
Financing Receivable, Past Due [Line Items]
Current	102,925	104,334
Total	105,030	106,956
Consumer Banking
Financing Receivable, Past Due [Line Items]
Current	74,117	65,445
Total	77,112	68,888
Consumer Banking | Auto
Financing Receivable, Past Due [Line Items]
Current	71,770	62,381
Total	74,716	65,762
Consumer Banking | Retail banking
Financing Receivable, Past Due [Line Items]
Current	2,347	3,064
Total	2,396	3,126
Commercial Banking
Financing Receivable, Past Due [Line Items]
Current	78,781	75,281
Total	79,248	75,780
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Past Due [Line Items]
Current	32,973	30,340
Total	33,096	30,681
Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Current	45,808	44,941
Total	$ 46,152	$ 45,099
30-59 days
Financing Receivable, Past Due [Line Items]
Past due, percentage of total loans	1.14%	1.32%
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 2,993	$ 3,330
30-59 days | Credit Card
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	718	845
30-59 days | Consumer Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	2,022	2,280
30-59 days | Consumer Banking | Auto
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	1,996	2,252
30-59 days | Consumer Banking | Retail banking
Financing Receivable, Past Due [Line Items]
Total	26	28
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	26	28
30-59 days | Commercial Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	253	205
30-59 days | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	72	136
30-59 days | Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 181	$ 69
60-89 days
Financing Receivable, Past Due [Line Items]
Past due, percentage of total loans	0.53%	0.59%
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 1,379	$ 1,485
60-89 days | Credit Card
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	470	522
60-89 days | Consumer Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	774	926
60-89 days | Consumer Banking | Auto
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	769	907
60-89 days | Consumer Banking | Retail banking
Financing Receivable, Past Due [Line Items]
Total	5	19
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	5	19
60-89 days | Commercial Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	135	37
60-89 days | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	1	22
60-89 days | Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 134	$ 15
Greater than 90 days
Financing Receivable, Past Due [Line Items]
Past due, percentage of total loans	0.46%	0.70%
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 1,195	$ 1,749
Greater than 90 days | Credit Card
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	917	1,255
Greater than 90 days | Consumer Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	199	237
Greater than 90 days | Consumer Banking | Auto
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	181	222
Greater than 90 days | Consumer Banking | Retail banking
Financing Receivable, Past Due [Line Items]
Total	18	15
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	18	15
Greater than 90 days | Commercial Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	79	257
Greater than 90 days | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	50	183
Greater than 90 days | Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 29	$ 74
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Past due total, percentatge of total loans	2.13%	2.61%
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 5,567	$ 6,564
Financial Asset, Past Due | Credit Card
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	2,105	2,622
Financial Asset, Past Due | Consumer Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	2,995	3,443
Financial Asset, Past Due | Consumer Banking | Auto
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	2,946	3,381
Financial Asset, Past Due | Consumer Banking | Retail banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	49	62
Financial Asset, Past Due | Commercial Banking
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	467	499
Financial Asset, Past Due | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	123	341
Financial Asset, Past Due | Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	344	158
Domestic credit card: | Credit Card
Financing Receivable, Past Due [Line Items]
Current	97,346	96,116
Total	99,258	98,504
Domestic credit card: | 30-59 days | Credit Card
Financing Receivable, Past Due [Line Items]
Total	646	755
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	646	755
Domestic credit card: | 60-89 days | Credit Card
Financing Receivable, Past Due [Line Items]
Total	425	464
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	425	464
Domestic credit card: | Greater than 90 days | Credit Card
Financing Receivable, Past Due [Line Items]
Total	841	1,169
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	841	1,169
Domestic credit card: | Financial Asset, Past Due | Credit Card
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	1,912	2,388
International card businesses: | Credit Card
Financing Receivable, Past Due [Line Items]
Current	5,579	8,218
Total	5,772	8,452
International card businesses: | 30-59 days | Credit Card
Financing Receivable, Past Due [Line Items]
Total	72	90
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	72	90
International card businesses: | 60-89 days | Credit Card
Financing Receivable, Past Due [Line Items]
Total	45	58
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	45	58
International card businesses: | Greater than 90 days | Credit Card
Financing Receivable, Past Due [Line Items]
Total	76	86
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	76	86
International card businesses: | Financial Asset, Past Due | Credit Card
Financing Receivable, Past Due [Line Items]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Noncurrent	$ 193	$ 234