Loan Portfolio (Details) - USD ($)	Jun. 30, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 107,078,000,000	$ 112,606,000,000
Accrued interest	502,000,000	522,000,000
Discontinued operations | Education Lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	291,000,000	339,000,000
Total commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	73,525,000,000	77,591,000,000
Accrued interest	365,000,000	383,000,000
Total commercial loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	53,129,000,000	55,815,000,000
Total commercial loans | Commercial and industrial | Collateral Pledged
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	285,000,000	0
Total commercial loans | Total commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,295,000,000	18,253,000,000
Total commercial loans | Commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,218,000,000	15,187,000,000
Total commercial loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,077,000,000	3,066,000,000
Total commercial loans | Commercial lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,101,000,000	3,523,000,000
Total commercial loans | Commercial lease financing | Collateral Pledged
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,000,000	7,000,000
Total commercial loans | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	217,000,000	207,000,000
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	33,553,000,000	35,015,000,000
Accrued interest	137,000,000	139,000,000
Total consumer loans | Total residential — prime loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	27,109,000,000	28,097,000,000
Total consumer loans | Real estate — residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	20,380,000,000	20,958,000,000
Total consumer loans | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,729,000,000	7,139,000,000
Total consumer loans | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,514,000,000	5,916,000,000
Total consumer loans | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	930,000,000	1,002,000,000
Total consumer loans | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 930,000,000	$ 1,002,000,000