Loans - Consumer, Excluding Credit Card Loan Portfolio, Residential Real Estate, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 948,642,000,000	$ 1,003,089,000,000	$ 960,506,000,000
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	302,392,000,000	293,779,000,000	302,127,000,000
Consumer, excluding credit card | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	5,247,000,000		5,313,000,000
Retained loans	$ 219,173,000,000		$ 225,302,000,000
Weighted average LTV ratio	53.00%		54.00%
Weighted average FICO	$ 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	$ 45,000,000	$ 43,000,000
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	30,000,000		33,000,000
Retained loans	76,000,000		76,000,000
Consumer, excluding credit card | Residential real estate | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	70,787,000,000		73,444,000,000
Consumer, excluding credit card | Residential real estate | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	32,042,000,000		32,287,000,000
Consumer, excluding credit card | Residential real estate | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,086,000,000		13,981,000,000
Consumer, excluding credit card | Residential real estate | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,320,000,000		13,773,000,000
Consumer, excluding credit card | Residential real estate | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	12,350,000,000		13,130,000,000
Consumer, excluding credit card | Residential real estate | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,085,000,000		8,235,000,000
Consumer, excluding credit card | Residential real estate | Washington
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,687,000,000		7,917,000,000
Consumer, excluding credit card | Residential real estate | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6,934,000,000		7,227,000,000
Consumer, excluding credit card | Residential real estate | Massachusetts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,715,000,000		5,784,000,000
Consumer, excluding credit card | Residential real estate | Connecticut
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,012,000,000		5,024,000,000
Consumer, excluding credit card | Residential real estate | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	43,155,000,000		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	76,000,000		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
Consumer, excluding credit card | Residential real estate | No FICO/LTV available
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,713,000,000		1,732,000,000
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	19,000,000		10,000,000
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	14,000,000		18,000,000
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	105,000,000		72,000,000
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	46,000,000		65,000,000
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	1,482,000,000		2,365,000,000
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	286,000,000		435,000,000
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	204,165,000,000		208,457,000,000
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	$ 11,267,000,000		$ 12,072,000,000