Loan Portfolio - Loans by Category (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 100,926	$ 101,185
Accrued interest	242	241
Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	71,414	71,980
Accrued interest	143	140
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	29,512	29,205
Accrued interest	98	101
Commercial and Industrial | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	52,486	52,907
Commercial mortgage | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	12,702	12,687
Construction | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,122	1,987
Commercial real estate loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,824	14,674
Commercial lease financing | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,104	4,399
Real estate — residential mortgage | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,300	9,298
Home equity loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,158	9,360
Residential - Prime Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	19,458	18,658
Consumer direct loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,862	4,714
Credit cards | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	909	989
Consumer indirect loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,283	4,844
Commercial credit card | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	126	127
Commercial credit card | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	909	989
Collateral pledged | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	21	23
Education Lending | Discontinued Operations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 675	$ 710