Loan Portfolio - Loans by Category (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 98,609	$ 101,185
Accrued interest	211	241
Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	69,329	71,980
Accrued interest	117	140
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	29,280	29,205
Accrued interest	95	101
Commercial and Industrial | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	49,553	52,907
Commercial mortgage | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,674	12,687
Construction | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,120	1,987
Commercial real estate loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,794	14,674
Commercial lease financing | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,982	4,399
Real estate — residential mortgage | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,204	9,298
Home equity loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,747	9,360
Residential - Prime Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	22,951	18,658
Consumer direct loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,324	4,714
Credit cards | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	928	989
Consumer indirect loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	77	4,844
Commercial credit card | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	139	127
Commercial credit card | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	928	989
Collateral pledged | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	16	23
Education Lending | Discontinued Operations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 602	$ 710