Loans - Consumer, Excluding Credit Card Loan Portfolio, Residential Real Estate, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	$ 960,506,000,000	$ 945,601,000,000	$ 969,415,000,000
Consumer, excluding credit card
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	302,127,000,000	294,999,000,000	$ 335,776,000,000
Consumer, excluding credit card | Residential real estate
Loans and Leases Receivable Disclosure [Line Items]
Nonaccrual loans	5,313,000,000	2,780,000,000
Retained loans	$ 225,302,000,000	$ 243,317,000,000
Weighted average LTV ratio	54.00%	55.00%
Weighted average FICO	$ 763	$ 758
Approximate percentage of Chapter 7 loans 30 days or more past due	7.00%
Interest income on nonaccrual loans recognized on a cash basis	$ 161,000,000	166,000,000
Consumer, excluding credit card | Residential real estate | U.S. government-guaranteed
Loans and Leases Receivable Disclosure [Line Items]
90 or more days past due and still accruing	33,000,000	38,000,000
Retained loans	76,000,000	63,000,000
Consumer, excluding credit card | Residential real estate | Residential real estate – PCD
Loans and Leases Receivable Disclosure [Line Items]
Nonaccrual loans	1,600,000,000
Consumer, excluding credit card | Residential real estate | 90 or more days past due
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	0	0
Consumer, excluding credit card | Residential real estate | 90 or more days past due | U.S. government-guaranteed
Loans and Leases Receivable Disclosure [Line Items]
Nonaccrual loans	33,000,000	34,000,000
Consumer, excluding credit card | Residential real estate | California
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	73,444,000,000	82,147,000,000
Consumer, excluding credit card | Residential real estate | New York
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	32,287,000,000	31,996,000,000
Consumer, excluding credit card | Residential real estate | Florida
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	13,981,000,000	13,668,000,000
Consumer, excluding credit card | Residential real estate | Texas
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	13,773,000,000	14,474,000,000
Consumer, excluding credit card | Residential real estate | Illinois
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	13,130,000,000	15,587,000,000
Consumer, excluding credit card | Residential real estate | Colorado
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	8,235,000,000	8,447,000,000
Consumer, excluding credit card | Residential real estate | Washington
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	7,917,000,000	8,990,000,000
Consumer, excluding credit card | Residential real estate | New Jersey
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	7,227,000,000	7,752,000,000
Consumer, excluding credit card | Residential real estate | Massachusetts
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	5,784,000,000	6,210,000,000
Consumer, excluding credit card | Residential real estate | Connecticut
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	5,024,000,000	4,954,000,000
Consumer, excluding credit card | Residential real estate | All other
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	44,500,000,000	49,092,000,000
Consumer, excluding credit card | Residential real estate | All other | U.S. government-guaranteed
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	76,000,000	63,000,000
Consumer, excluding credit card | Residential real estate | No FICO/LTV available
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	1,732,000,000	2,052,000,000
Consumer, excluding credit card | Residential real estate | Greater than 125% and refreshed FICO scores | Equal to or greater than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	10,000,000	31,000,000
Consumer, excluding credit card | Residential real estate | Greater than 125% and refreshed FICO scores | Less than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	18,000,000	38,000,000
Consumer, excluding credit card | Residential real estate | 101% to 125% and refreshed FICO scores | Equal to or greater than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	72,000,000	134,000,000
Consumer, excluding credit card | Residential real estate | 101% to 125% and refreshed FICO scores | Less than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	65,000,000	132,000,000
Consumer, excluding credit card | Residential real estate | 80% to 100% and refreshed FICO scores | Equal to or greater than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	2,365,000,000	5,953,000,000
Consumer, excluding credit card | Residential real estate | 80% to 100% and refreshed FICO scores | Less than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	435,000,000	764,000,000
Consumer, excluding credit card | Residential real estate | Lower than 80% and refreshed FICO scores | Equal to or greater than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	208,457,000,000	219,469,000,000
Consumer, excluding credit card | Residential real estate | Lower than 80% and refreshed FICO scores | Less than 660
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	$ 12,072,000,000	$ 14,681,000,000