Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual and Other Credit Quality Indicators and Loan Modifications (Details) - USD ($)	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 1,273,047,000,000	$ 1,280,870,000,000	$ 1,255,688,000,000
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	382,795,000,000	397,275,000,000	$ 396,195,000,000
Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	192,000,000	177,000,000
Total retained loans	67,952,000,000	70,866,000,000
Commitments to lend to borrowers experiencing financial difficulty	0	0
Consumer, excluding credit card | Auto and other | California
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	10,433,000,000	10,959,000,000
Consumer, excluding credit card | Auto and other | Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	8,025,000,000	8,502,000,000
Consumer, excluding credit card | Auto and other | Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	5,507,000,000	5,684,000,000
Consumer, excluding credit card | Auto and other | New York
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	4,910,000,000	4,938,000,000
Consumer, excluding credit card | Auto and other | Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,977,000,000	3,147,000,000
Consumer, excluding credit card | Auto and other | New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,505,000,000	2,609,000,000
Consumer, excluding credit card | Auto and other | Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,962,000,000	1,900,000,000
Consumer, excluding credit card | Auto and other | Georgia
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,789,000,000	1,912,000,000
Consumer, excluding credit card | Auto and other | Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,673,000,000	1,779,000,000
Consumer, excluding credit card | Auto and other | North Carolina
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,630,000,000	1,714,000,000
Consumer, excluding credit card | Auto and other | All other
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 26,541,000,000	$ 27,722,000,000