Loans - TDR - Subsequent Defaults (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) contract	Mar. 31, 2020 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	24,372	30,025
Total Loans | $	$ 67	$ 92
Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	22,336	28,743
Total Loans | $	$ 38	$ 48
Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	2,036	1,276
Total Loans | $	$ 29	$ 16
Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	2,031	1,275
Total Loans | $	$ 29	$ 16
Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	5	1
Total Loans | $	$ 0	$ 0
Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	0	6
Total Loans | $	$ 0	$ 28
Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	0	6
Total Loans | $	$ 0	$ 28
Domestic credit card: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	5,134	10,886
Total Loans | $	$ 10	$ 22
International card businesses: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	17,202	17,857
Total Loans | $	$ 28	$ 26