Loans - Credit Card Delinquency Status (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	$ 261,390	$ 251,624
Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	104,572	106,323
Revolving loans converted to term	458	633
Total	105,030	106,956
Domestic credit card: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	98,858	97,969
Revolving loans converted to term	400	535
Total	99,258	98,504
International card businesses: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	5,714	8,354
Revolving loans converted to term	58	98
Total	5,772	8,452
Current | Domestic credit card: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	96,977	95,629
Revolving loans converted to term	369	487
Total	97,346	96,116
Current | International card businesses: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	5,534	8,152
Revolving loans converted to term	45	66
Total	5,579	8,218
30-59 days | Domestic credit card: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	632	734
Revolving loans converted to term	14	21
Total	646	755
30-59 days | International card businesses: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	67	79
Revolving loans converted to term	5	11
Total	72	90
60-89 days | Domestic credit card: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	417	451
Revolving loans converted to term	8	13
Total	425	464
60-89 days | International card businesses: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	41	47
Revolving loans converted to term	4	11
Total	45	58
Greater than 90 days | Domestic credit card: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	832	1,155
Revolving loans converted to term	9	14
Total	841	1,169
Greater than 90 days | International card businesses: | Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans	72	76
Revolving loans converted to term	4	10
Total	$ 76	$ 86