Loan Portfolio (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 109,885	$ 112,606
Accrued interest	508	522
Discontinued operations | Education Lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	313	339
Total commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	75,651	77,591
Accrued interest	368	383
Total commercial loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	54,793	55,815
Total commercial loans | Commercial and industrial | Collateral Pledged
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	349
Total commercial loans | Total commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,553	18,253
Total commercial loans | Commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,540	15,187
Total commercial loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,013	3,066
Total commercial loans | Commercial lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,305	3,523
Total commercial loans | Commercial lease financing | Collateral Pledged
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6	7
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	34,234	35,015
Accrued interest	140	139
Total consumer loans | Total residential — prime loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	27,609	28,097
Total consumer loans | Real estate — residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	20,704	20,958
Total consumer loans | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,905	7,139
Total consumer loans | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,690	5,916
Total consumer loans | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 935	$ 1,002