Loan Portfolio - Loans by Category (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 100,730	$ 101,185
Accrued interest	225	241
Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	69,830	71,980
Accrued interest	127	140
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	30,900	29,205
Accrued interest	97	101
Commercial and Industrial | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	50,672	52,907
Commercial mortgage | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	12,965	12,687
Construction | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,132	1,987
Commercial real estate loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,097	14,674
Commercial lease financing | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,061	4,399
Real estate — residential mortgage | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	12,131	9,298
Home equity loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,047	9,360
Residential - Prime Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	21,178	18,658
Consumer direct loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,049	4,714
Credit cards | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	923	989
Consumer indirect loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,750	4,844
Commercial credit card | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	135	127
Commercial credit card | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	923	989
Collateral pledged | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	19	23
Education Lending | Discontinued Operations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 636	$ 710