Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	$ 974,260,000,000	$ 960,506,000,000	$ 945,537,000,000
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	298,308,000,000	302,127,000,000	$ 305,106,000,000
Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	117,000,000	151,000,000
Retained loans	76,637,000,000	76,825,000,000
90 or more days past due and still accruing	0	0
Consumer, excluding credit card | Auto and other | California
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	12,137,000,000	12,302,000,000
Consumer, excluding credit card | Auto and other | Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	8,333,000,000	8,235,000,000
Consumer, excluding credit card | Auto and other | New York
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	7,511,000,000	8,824,000,000
Consumer, excluding credit card | Auto and other | Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	5,125,000,000	4,668,000,000
Consumer, excluding credit card | Auto and other | Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	3,333,000,000	3,768,000,000
Consumer, excluding credit card | Auto and other | New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	2,580,000,000	2,646,000,000
Consumer, excluding credit card | Auto and other | Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	2,103,000,000	2,465,000,000
Consumer, excluding credit card | Auto and other | Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	2,076,000,000	1,924,000,000
Consumer, excluding credit card | Auto and other | Ohio
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	2,029,000,000	2,163,000,000
Consumer, excluding credit card | Auto and other | Louisiana
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	1,870,000,000	1,808,000,000
Consumer, excluding credit card | Auto and other | All other
Financing Receivable, Credit Quality Indicator [Line Items]
Retained loans	$ 29,540,000,000	$ 28,022,000,000