Allowance for Loan and Lease Losses (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Special provision due to hurricane	$ 32.4
Special provision due to hurricane, originated loans portfolio	17.5
Special provision due to hurricane, originated mortgage loans portfolio	3.8
Special provision due to hurricane, originated auto loans portfolio	4.7
Special provision due to hurricane, originated commercial loans portfolio	7.3
Special provision due to hurricane, originated consumer loans portfolio	1.7
Special provision due to hurricane, acquired loans portfolio	14.9
Special provision due to hurricane, acquired mortgage loans portfolio	6.7
Special provision due to hurricane, acquired commercial loans portfolio	7.9
Special provision due to hurricane, acquired auto loans portfolio	$ 0.3