Loans - TDR - Subsequent Defaults (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) Contract	Jun. 30, 2019 USD ($) Contract	Jun. 30, 2020 USD ($) Contract	Jun. 30, 2019 USD ($) Contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	27,954	31,082	57,979	62,928
Total Loans | $	$ 78	$ 71	$ 170	$ 141
Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	27,090	29,766	55,833	60,499
Total Loans | $	$ 46	$ 54	$ 94	$ 111
Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	863	1,316	2,139	2,429
Total Loans | $	$ 11	$ 17	$ 27	$ 30
Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	860	1,312	2,135	2,417
Total Loans | $	$ 11	$ 16	$ 27	$ 29
Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	3	4	4	12
Total Loans | $	$ 0	$ 1	$ 0	$ 1
Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	1	0	7	0
Total Loans | $	$ 21	$ 0	$ 49	$ 0
Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	1	0	7	0
Total Loans | $	$ 21	$ 0	$ 49	$ 0
Domestic credit card: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	9,582	11,581	20,468	25,608
Total Loans | $	$ 21	$ 26	$ 43	$ 55
International card businesses: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	17,508	18,185	35,365	34,891
Total Loans | $	$ 25	$ 28	$ 51	$ 56