Loans - Consumer, Excluding Credit Card Loan Portfolio, Residential Real Estate, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 963,665,000,000	$ 965,448,000,000	$ 963,665,000,000	$ 965,448,000,000	$ 960,506,000,000
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	297,731,000,000	307,005,000,000	297,731,000,000	307,005,000,000	302,127,000,000
Consumer, excluding credit card | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	5,060,000,000		5,060,000,000		5,313,000,000
Retained loans	$ 218,031,000,000		$ 218,031,000,000		$ 225,302,000,000
Weighted average LTV ratio	53.00%		53.00%		54.00%
Weighted average FICO	$ 764		$ 764		$ 763
Approximate percentage of Chapter 7 loans 30 days or more past due			7.00%
Interest income on nonaccrual loans recognized on a cash basis	41,000,000	$ 37,000,000	$ 86,000,000	$ 80,000,000
Consumer, excluding credit card | Residential real estate | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 or more days past due	49,000,000		49,000,000		33,000,000
Retained loans	72,000,000		72,000,000		76,000,000
Consumer, excluding credit card | Residential real estate | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	69,856,000,000		69,856,000,000		73,444,000,000
Consumer, excluding credit card | Residential real estate | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	31,921,000,000		31,921,000,000		32,287,000,000
Consumer, excluding credit card | Residential real estate | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,655,000,000		14,655,000,000		13,981,000,000
Consumer, excluding credit card | Residential real estate | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,284,000,000		13,284,000,000		13,773,000,000
Consumer, excluding credit card | Residential real estate | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	12,036,000,000		12,036,000,000		13,130,000,000
Consumer, excluding credit card | Residential real estate | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,113,000,000		8,113,000,000		8,235,000,000
Consumer, excluding credit card | Residential real estate | Washington
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,788,000,000		7,788,000,000		7,917,000,000
Consumer, excluding credit card | Residential real estate | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6,864,000,000		6,864,000,000		7,227,000,000
Consumer, excluding credit card | Residential real estate | Massachusetts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,829,000,000		5,829,000,000		5,784,000,000
Consumer, excluding credit card | Residential real estate | Connecticut
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,010,000,000		5,010,000,000		5,024,000,000
Consumer, excluding credit card | Residential real estate | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	42,675,000,000		42,675,000,000		44,500,000,000
Consumer, excluding credit card | Residential real estate | All other | U.S. government-guaranteed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	72,000,000		72,000,000		76,000,000
Consumer, excluding credit card | Residential real estate | 90 or more days past due and still accruing interest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0		0		0
Consumer, excluding credit card | Residential real estate | No FICO/LTV available
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,633,000,000		4,633,000,000		2,492,000,000
Consumer, excluding credit card | Residential real estate | Greater than 125% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,000,000		4,000,000		6,000,000
Consumer, excluding credit card | Residential real estate | Greater than 125% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,000,000		7,000,000		12,000,000
Consumer, excluding credit card | Residential real estate | 101% to 125% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	24,000,000		24,000,000		38,000,000
Consumer, excluding credit card | Residential real estate | 101% to 125% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	26,000,000		26,000,000		44,000,000
Consumer, excluding credit card | Residential real estate | 80% to 100% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,793,000,000		1,793,000,000		2,177,000,000
Consumer, excluding credit card | Residential real estate | 80% to 100% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	132,000,000		132,000,000		239,000,000
Consumer, excluding credit card | Residential real estate | Lower than 80% and refreshed FICO scores | Equal to or greater than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	200,924,000,000		200,924,000,000		208,238,000,000
Consumer, excluding credit card | Residential real estate | Lower than 80% and refreshed FICO scores | Less than 660
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 10,416,000,000		$ 10,416,000,000		$ 11,980,000,000