Loans - TDR - Subsequent Defaults (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) contract	Sep. 30, 2020 USD ($) contract	Sep. 30, 2021 USD ($) contract	Sep. 30, 2020 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	19,001	18,541	64,707	76,520
Total Loans | $	$ 96	$ 63	$ 361	$ 233
Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	16,848	17,227	58,237	73,060
Total Loans | $	$ 24	$ 31	$ 93	$ 125
Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	2,152	1,310	6,462	3,449
Total Loans | $	$ 34	$ 16	$ 98	$ 43
Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	2,151	1,307	6,453	3,442
Total Loans | $	$ 34	$ 15	$ 98	$ 42
Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1	3	9	7
Total Loans | $	$ 0	$ 1	$ 0	$ 1
Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1	4	8	11
Total Loans | $	$ 38	$ 16	$ 170	$ 65
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	0	0	1	0
Total Loans | $	$ 0	$ 0	$ 50	$ 0
Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1	4	7	11
Total Loans | $	$ 38	$ 16	$ 120	$ 65
Domestic credit card: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	4,168	6,554	13,528	27,022
Total Loans | $	$ 7	$ 14	$ 25	$ 57
International card businesses: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	12,680	10,673	44,709	46,038
Total Loans | $	$ 17	$ 17	$ 68	$ 68