Loans - Trouble Debt Restructurings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 179	$ 481	$ 601	$ 1,185
Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	65	89	208	313
Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	89	134	270	398
Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	89	133	269	393
Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified		1	1	5
Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	25	258	123	474
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	21	57	41	85
Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 4	$ 201	$ 82	$ 389
Reduced Interest Rate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	61.00%	19.00%	53.00%	29.00%
Average Rate Reduction	68.95%	20.08%	16.84%	18.49%
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	20.90%	20.94%	21.26%	20.22%
Reduced Interest Rate | Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	48.00%	4.00%	40.00%	9.00%
Average Rate Reduction	8.54%	4.75%	8.72%	3.76%
Reduced Interest Rate | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	48.00%	3.00%	40.00%	9.00%
Average Rate Reduction	8.54%	4.83%	8.74%	3.68%
Reduced Interest Rate | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		85.00%	20.00%	9.00%
Average Rate Reduction		3.24%	2.55%	10.85%
Reduced Interest Rate | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	12.00%	0.00%	2.00%	0.00%
Average Rate Reduction	2.50%	0.00%	1.29%	0.00%
Reduced Interest Rate | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	14.00%	0.00%	7.00%	0.00%
Average Rate Reduction	2.50%	0.00%	1.29%	0.00%
Reduced Interest Rate | Commercial Banking | Commercial And Industrial [Member]
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	59.00%	61.00%	54.00%	56.00%
Average Term Extension (Months)	6 months	14 months	5 months	9 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	92.00%	94.00%	93.00%	94.00%
Average Term Extension (Months)	4 months	2 months	4 months	3 months
Term Extension | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	92.00%	94.00%	93.00%	95.00%
Average Term Extension (Months)	4 months	2 months	4 months	3 months
Term Extension | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		15.00%	36.00%	15.00%
Average Term Extension (Months)		61 months	67 months	8 months
Term Extension | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	100.00%	64.00%	61.00%	61.00%
Average Term Extension (Months)	11 months	23 months	11 months	16 months
Term Extension | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	100.00%	100.00%	100.00%	100.00%
Average Term Extension (Months)	12 months	4 months	13 months	6 months
Term Extension | Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity	100.00%	54.00%	41.00%	52.00%
Average Term Extension (Months)	4 months	32 months	8 months	21 months
Principal Forgiveness
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	1.00%
Gross Balance Reduction		$ 1	$ 1	$ 8
Principal Forgiveness | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Gross Balance Reduction		$ 0	$ 0	$ 0
Principal Forgiveness | Consumer Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Gross Balance Reduction		$ 1	$ 1	$ 1
Principal Forgiveness | Consumer Banking | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Gross Balance Reduction		$ 1	$ 1	$ 1
Principal Forgiveness | Consumer Banking | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	0.00%
Gross Balance Reduction		$ 0	$ 0	$ 0
Principal Forgiveness | Commercial Banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	3.00%
Gross Balance Reduction		$ 0	$ 0	$ 7
Principal Forgiveness | 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
Principal Forgiveness | Commercial Banking | Commercial And Industrial [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of TDR Activity		0.00%	0.00%	4.00%
Gross Balance Reduction		$ 0	$ 0	$ 7
Domestic credit card: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 37	$ 50	$ 114	$ 195
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	15.80%	15.53%	16.00%	15.92%
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%	0.00%
Gross Balance Reduction		$ 0	$ 0	$ 0
International card businesses: | Credit Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans Modified	$ 28	$ 39	$ 94	$ 118
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	27.75%	27.89%	27.66%	27.33%
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%	0.00%
Gross Balance Reduction		$ 0	$ 0	$ 0