Loans and Leases - Schedule of Allowance for Loan Losses (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 23,294.0	$ 19,757.0
Loans and leases, allowance for losses	54.0	53.0
Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	22,533.0	18,888.0
Loans and leases, allowance for losses		0.2
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	98.0	27.0
Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	663.0	842.0
Individually evaluated for impairment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0.0	15.0
Individually evaluated for impairment | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0.0	15.0
Individually evaluated for impairment | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0.0	0.0
Individually evaluated for impairment | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0.0	0.0
Collectively evaluated for impairment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	23,294.0	19,742.0
Collectively evaluated for impairment | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	22,533.0	18,873.0
Collectively evaluated for impairment | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	98.0	27.0
Collectively evaluated for impairment | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 663.0	$ 842.0