Loans and Leases - Recorded Investment in Each Class of Total Loans and Leases by Credit Quality Indicator (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 29,582	$ 23,294
Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	28,661	22,533
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	257	98
Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	664	663
Investment grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	24,486	18,627
Investment grade | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	23,565	17,866
Investment grade | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	257	98
Investment grade | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	664	663
Speculative
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	5,096	4,638
Speculative | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	5,096	4,638
Speculative | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Speculative | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 0	0
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases		29
Special Mention | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases		29
Special Mention | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases		0
Special Mention | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases		$ 0