Fair Value Measurements (Nonrecurring Basis Significant Unobservable Inputs) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 12.6	$ 6.7	$ 6.7
Valuation Technique	Market Approach	Market Approach
Unobservable Input	Discount to reflect realizable value	Discount to reflect realizable value
OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 1.4	$ 0.7	$ 1.8
Valuation Technique	Market Approach	Market Approach
Unobservable Input	Discount to reflect realizable value	Discount to reflect realizable value
Lower Limit | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range of Discounts Applied	15.00%	15.00%
Lower Limit | OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range of Discounts Applied	15.00%	15.00%
Upper Limit | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range of Discounts Applied	25.00%	25.00%
Upper Limit | OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range of Discounts Applied	20.00%	20.00%