Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual Loans and Other Credit Quality Indicators (Details) (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	$ 960,506,000,000	$ 945,601,000,000	$ 969,415,000,000
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	302,127,000,000	294,999,000,000	$ 335,776,000,000
Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	151,000,000	146,000,000
Retained loans	76,825,000,000	51,682,000,000
90 or more days past due and still accruing	0	0
California | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	12,302,000,000	7,795,000,000
New York | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	8,824,000,000	3,706,000,000
Texas | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	8,235,000,000	5,457,000,000
Florida | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	4,668,000,000	3,025,000,000
Illinois | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	3,768,000,000	2,443,000,000
New Jersey | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	2,646,000,000	1,798,000,000
Arizona | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	2,465,000,000	1,347,000,000
Ohio | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	2,163,000,000	1,490,000,000
Pennsylvania | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	1,924,000,000	1,721,000,000
Colorado | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	1,910,000,000	1,247,000,000
All other | Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	$ 27,920,000,000	$ 21,653,000,000