Loan Portfolio - Loans by Category (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 103,081	$ 94,646
Accrued interest	235	244
Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	74,481	68,032
Accrued interest	133
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	28,600	26,614
Accrued interest	102
Commercial and industrial | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	55,025	48,295
Commercial mortgage | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,059	13,491
Real estate — construction | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,947	1,558
Commercial real estate loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,006	15,049
Commercial lease financing | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,450	4,688
Real estate — residential mortgage | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,715	7,023
Home equity loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,488	10,274
Residential - Prime Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	18,203	17,297
Consumer direct loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	4,395	3,513
Credit cards | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	970	1,130
Consumer indirect loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,032	4,674
Credit cards | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	128	144
Credit cards | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	970	1,130
Collateral pledged | Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	18	15
Education Lending | Discontinued operations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 743	$ 865