Loans - Trouble Debt Restructurings (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 160	$ 412	$ 422	$ 704
Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	60	84	143	224
Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	66	138	181	264
Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	65	137	180	260
Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	1	1	1	4
Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	34	190	98	216
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	0	9	20	28
Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 34	$ 181	$ 78	$ 188
Reduced Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	53.00%	22.00%	49.00%	36.00%
Average Rate Reduction	9.38%	17.96%	8.64%	17.90%
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	21.22%	19.14%	21.43%	19.94%
Reduced Interest Rate | Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	38.00%	5.00%	36.00%	12.00%
Average Rate Reduction	8.62%	4.19%	8.85%	3.55%
Reduced Interest Rate | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	39.00%	5.00%	36.00%	12.00%
Average Rate Reduction	8.62%	4.12%	8.87%	3.51%
Reduced Interest Rate | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	10.00%	31.00%	4.00%
Average Rate Reduction	0.00%	8.37%	3.77%	11.42%
Reduced Interest Rate | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Rate Reduction	0.00%	0.00%	0.00%	0.00%
Reduced Interest Rate | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Rate Reduction	0.00%	0.00%	0.00%	0.00%
Reduced Interest Rate | Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Rate Reduction	0.00%	0.00%	0.00%	0.00%
Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	49.00%	57.00%	52.00%	52.00%
Average Term Extension (Months)	3 months	5 months	3 months	5 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	91.00%	95.00%	94.00%	93.00%
Average Term Extension (Months)	4 months	3 months	3 months	4 months
Term Extension | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	91.00%	95.00%	94.00%	95.00%
Average Term Extension (Months)	4 months	3 months	3 months	4 months
Term Extension | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	100.00%	59.00%	69.00%	15.00%
Average Term Extension (Months)	41 months	4 months	28 months	4 months
Term Extension | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	56.00%	55.00%	51.00%	57.00%
Average Term Extension (Months)	17 months	8 months	11 months	9 months
Term Extension | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	0.00%	100.00%	100.00%	100.00%
Average Term Extension (Months)	0 months	7 months	14 months	10 months
Term Extension | Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	56.00%	52.00%	38.00%	50.00%
Average Term Extension (Months)	17 months	8 months	8 months	8 months
Principal Forgiveness
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		4.00%		2.00%
Gross Balance Reduction		$ 7		$ 7
Principal Forgiveness | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%		0.00%
Gross Balance Reduction		$ 0		$ 0
Principal Forgiveness | Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%		0.00%
Gross Balance Reduction		$ 0		$ 0
Principal Forgiveness | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%		0.00%
Gross Balance Reduction		$ 0		$ 0
Principal Forgiveness | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%		0.00%
Gross Balance Reduction		$ 0		$ 0
Principal Forgiveness | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		8.00%		7.00%
Gross Balance Reduction		$ 7		$ 7
Principal Forgiveness | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%		0.00%
Gross Balance Reduction		$ 0		$ 0
Principal Forgiveness | Commercial Banking | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		9.00%		8.00%
Gross Balance Reduction		$ 7		$ 7
Domestic credit card: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 33	$ 56	$ 77	$ 145
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	16.07%	15.41%	16.10%	16.05%
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: | Principal Forgiveness | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%		0.00%
Gross Balance Reduction		$ 0		$ 0
International card businesses: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 27	$ 28	$ 66	$ 79
International card businesses: | 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	27.45%	26.56%	27.62%	27.05%
International card businesses: | 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 businesses: | Principal Forgiveness | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%		0.00%
Gross Balance Reduction		$ 0		$ 0