Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual and Other Credit Quality Indicators and Loan Modifications (Details) - USD ($)	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 1,285,370,000,000	$ 1,280,870,000,000	$ 1,265,941,000,000
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	377,938,000,000	397,275,000,000	$ 397,054,000,000
Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	233,000,000	177,000,000
Total retained loans	66,600,000,000	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	10,281,000,000	10,959,000,000
Consumer, excluding credit card | Auto and other | Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	7,738,000,000	8,502,000,000
Consumer, excluding credit card | Auto and other | Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	5,391,000,000	5,684,000,000
Consumer, excluding credit card | Auto and other | New York
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	4,892,000,000	4,938,000,000
Consumer, excluding credit card | Auto and other | Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,903,000,000	3,147,000,000
Consumer, excluding credit card | Auto and other | New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,475,000,000	2,609,000,000
Consumer, excluding credit card | Auto and other | Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,983,000,000	1,900,000,000
Consumer, excluding credit card | Auto and other | Georgia
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,725,000,000	1,912,000,000
Consumer, excluding credit card | Auto and other | Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,635,000,000	1,779,000,000
Consumer, excluding credit card | Auto and other | North Carolina
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,593,000,000	1,714,000,000
Consumer, excluding credit card | Auto and other | All other
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 25,984,000,000	$ 27,722,000,000