Fair Value Accounting (Fair Value Inputs, Assets, Quantitative Information) (Details) - Level 3 - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Measurements, Recurring Basis | Other liabilities | Option pricing methods and Monte Carlo simulation | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings as defined in merger agreement	$ 11.8	$ 9.3
Fair Value, Measurements, Recurring Basis | Other liabilities | Option pricing methods and Monte Carlo simulation | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings as defined in merger agreement	$ 16.7	$ 14.2
Fair Value, Measurements, Recurring Basis | Visa Derivative | Discounted cash flow analysis | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated future monthly fees payable to the derivative counterparty, period	1 year	1 year
Fair Value, Measurements, Recurring Basis | Visa Derivative | Discounted cash flow analysis | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated future monthly fees payable to the derivative counterparty, period	5 years	5 years
Fair Value, Measurements, Recurring Basis | Trust preferred securities | Discounted cash flow analysis
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Credit spread embedded in discount rate	3.98%	4.42%
Fair Value, Measurements, Recurring Basis | Private equity investments | Internal valuation
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount for lack of liquidity		15.00%
Fair Value, Measurements, Recurring Basis | GGL / SBA Loans Servicing Asset | Discounted cash flow analysis
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	12.19%
Prepayment speeds	6.75%
Fair Value, Measurements, Nonrecurring Basis | Collateral dependent impaired loans | Third-party appraised value of collateral less estimated selling costs | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	0.00%	0.00%
Estimated selling costs	0.00%	0.00%
Fair Value, Measurements, Nonrecurring Basis | Collateral dependent impaired loans | Third-party appraised value of collateral less estimated selling costs | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	60.00%	52.00%
Estimated selling costs	10.00%	10.00%
Fair Value, Measurements, Nonrecurring Basis | Collateral dependent impaired loans | Third-party appraised value of collateral less estimated selling costs | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	43.00%	25.00%
Estimated selling costs	7.00%	7.00%
Fair Value, Measurements, Nonrecurring Basis | Other loans held for sale | Third-party appraised value of collateral less estimated selling costs | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	0.00%
Estimated selling costs	0.00%
Fair Value, Measurements, Nonrecurring Basis | Other loans held for sale | Third-party appraised value of collateral less estimated selling costs | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	85.00%
Estimated selling costs	10.00%
Fair Value, Measurements, Nonrecurring Basis | Other loans held for sale | Third-party appraised value of collateral less estimated selling costs | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	48.00%
Estimated selling costs	2.00%
Fair Value, Measurements, Nonrecurring Basis | Other real estate | Third-party appraised value of collateral less estimated selling costs | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	0.00%	0.00%
Estimated selling costs	0.00%	0.00%
Fair Value, Measurements, Nonrecurring Basis | Other real estate | Third-party appraised value of collateral less estimated selling costs | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	86.00%	10.00%
Estimated selling costs	10.00%	10.00%
Fair Value, Measurements, Nonrecurring Basis | Other real estate | Third-party appraised value of collateral less estimated selling costs | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	32.00%	5.00%
Estimated selling costs	7.00%	7.00%
Fair Value, Measurements, Nonrecurring Basis | Other assets held for sale | Third-party appraised value less estimated selling costs or BOV | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	15.00%	0.00%
Estimated selling costs	0.00%	0.00%
Fair Value, Measurements, Nonrecurring Basis | Other assets held for sale | Third-party appraised value less estimated selling costs or BOV | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	46.00%	81.00%
Estimated selling costs	10.00%	10.00%
Fair Value, Measurements, Nonrecurring Basis | Other assets held for sale | Third-party appraised value less estimated selling costs or BOV | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount to appraised value	22.00%	47.00%
Estimated selling costs	7.00%	7.00%