Loans - TDR - Subsequent Defaults (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) contract	Jun. 30, 2020 USD ($) contract	Jun. 30, 2021 USD ($) contract	Jun. 30, 2020 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	21,334	27,954	45,706	57,979
Total Loans | $	$ 198	$ 78	$ 265	$ 170
Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	19,053	27,090	41,389	55,833
Total Loans | $	$ 31	$ 46	$ 69	$ 94
Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	2,274	863	4,310	2,139
Total Loans | $	$ 35	$ 11	$ 64	$ 27
Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	2,271	860	4,302	2,135
Total Loans | $	$ 35	$ 11	$ 64	$ 27
Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	3	3	8	4
Total Loans | $	$ 0	$ 0	$ 0	$ 0
Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	7	1	7	7
Total Loans | $	$ 132	$ 21	$ 132	$ 49
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1	0	1	0
Total Loans | $	$ 50	$ 0	$ 50	$ 0
Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	6	1	6	7
Total Loans | $	$ 82	$ 21	$ 82	$ 49
Domestic credit card: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	4,226	9,582	9,360	20,468
Total Loans | $	$ 8	$ 21	$ 18	$ 43
International card businesses: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	14,827	17,508	32,029	35,365
Total Loans | $	$ 23	$ 25	$ 51	$ 51