Loans - TDR Disclosures in Progress Financial Impact of Modification (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 246	$ 271	$ 705	$ 809
Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	128	151	387	453
Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	67	47	197	165
Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	66	47	190	153
Consumer Banking | Home loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified				6
Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	1	0	7	6
Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	51	73	121	191
Commercial Banking | Total commercial lending
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified		72	120	188
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified		22	34	41
Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 51	50	86	147
Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified		$ 1	$ 1	$ 3
Reduced Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	65.00%	65.00%	72.00%	67.00%
Average Rate Reduction	16.70%	17.26%	16.08%	16.79%
Reduced Interest Rate | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	100.00%	100.00%	100.00%	100.00%
Average Rate Reduction	20.19%	19.35%	20.18%	19.25%
Reduced Interest Rate | Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	42.00%	52.00%	40.00%	53.00%
Average Rate Reduction	3.53%	3.93%	3.76%	3.94%
Reduced Interest Rate | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	42.00%	51.00%	41.00%	55.00%
Average Rate Reduction	3.51%	3.88%	3.70%	3.91%
Reduced Interest Rate | Consumer Banking | Home loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity				28.00%
Average Rate Reduction				1.78%
Reduced Interest Rate | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	9.00%	100.00%	10.00%	14.00%
Average Rate Reduction	9.30%	10.45%	10.73%	11.09%
Reduced Interest Rate | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	9.00%	0.00%	32.00%	0.00%
Average Rate Reduction	1.00%	0.00%	0.07%	1.19%
Reduced Interest Rate | Commercial Banking | Total commercial lending
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	32.00%	0.00%
Average Rate Reduction		0.00%	0.07%	1.19%
Reduced Interest Rate | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	100.00%	0.00%
Average Rate Reduction		0.00%	0.00%	0.00%
Reduced Interest Rate | Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	9.00%	0.00%	5.00%	0.00%
Average Rate Reduction	1.00%	0.00%	0.60%	1.19%
Reduced Interest Rate | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Average Rate Reduction		0.00%	0.00%	0.00%
Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	27.00%	22.00%	28.00%	30.00%
Average Term Extension (Months)	9 months	8 months	8 months	14 months
Term Extension | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Term Extension (Months)	0 months	0 months	0 months	0 months
Term Extension | Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	88.00%	85.00%	89.00%	86.00%
Average Term Extension (Months)	8 months	9 months	7 months	15 months
Term Extension | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	89.00%	85.00%	90.00%	87.00%
Average Term Extension (Months)	8 months	9 months	8 months	8 months
Term Extension | Consumer Banking | Home loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity				83.00%
Average Term Extension (Months)				214 months
Term Extension | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	5.00%	54.00%	48.00%
Average Term Extension (Months)	0 months	12 months	3 months	6 months
Term Extension | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	15.00%	28.00%	18.00%	53.00%
Average Term Extension (Months)	14 months	5 months	9 months	11 months
Term Extension | Commercial Banking | Total commercial lending
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		28.00%	18.00%	54.00%
Average Term Extension (Months)		5 months	9 months	11 months
Term Extension | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		61.00%	0.00%	79.00%
Average Term Extension (Months)		3 months	0 months	5 months
Term Extension | Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	15.00%	13.00%	25.00%	47.00%
Average Term Extension (Months)	14 months	8 months	9 months	14 months
Term Extension | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Average Term Extension (Months)		0 months	0 months	0 months
Balance Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	1.00%	0.00%
Gross Balance Reduction	$ 1	$ 0	$ 1	$ 1
Balance Reduction | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	1.00%	1.00%	2.00%	1.00%
Gross Balance Reduction	$ 1	$ 0	$ 1	$ 1
Balance Reduction | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	1.00%	1.00%	1.00%	1.00%
Gross Balance Reduction	$ 1	$ 0	$ 1	$ 1
Balance Reduction | Consumer Banking | Home loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity				0.00%
Gross Balance Reduction				$ 0
Balance Reduction | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	34.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Total commercial lending
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Gross Balance Reduction		$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Gross Balance Reduction		$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Gross Balance Reduction		$ 0	$ 0	$ 0
Domestic credit card | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 85	$ 105	$ 257	$ 314
Domestic credit card | Reduced Interest Rate | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	100.00%	100.00%	100.00%	100.00%
Average Rate Reduction	16.76%	16.01%	16.58%	15.88%
Domestic credit card | Term Extension | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Term Extension (Months)	0 months	0 months	0 months	0 months
Domestic credit card | Balance Reduction | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
International card business | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 43	$ 46	$ 130	$ 139
International card business | Reduced Interest Rate | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	100.00%	100.00%	100.00%	100.00%
Average Rate Reduction	27.08%	26.95%	27.25%	26.87%
International card business | Term Extension | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Term Extension (Months)	0 months	0 months	0 months	0 months
International card business | Balance Reduction | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0