Fair Value (Quantitative Information About Level 3 Fair Value Measurements-Recurring) (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated fair value - assets	$ 386.3	$ 769.0
Estimated fair value - liabilities	(125.2)	(120.6)
FDIC True-up liability
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated fair value - liabilities	$ (65.1)	$ (61.9)
Discount Rate	2.90%	3.20%
Consideration holdback liability
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated fair value - liabilities	$ (46.0)	$ (47.2)
Derivative liabilities — non qualifying
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated fair value - liabilities	(14.1)	(11.5)
Securities — AFS
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated fair value - assets	385.8	485.5
Securities carried at fair value with changes recorded in net income
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated fair value - assets	$ 0.4	$ 283.5
Discount Rate	31.10%
Prepayment Rate	10.90%
Default Rate	2.40%
Loss Severity	59.20%
Derivative assets — non qualifying
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Estimated fair value - assets	$ 0.1
Minimum | Consideration holdback liability
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate		1.30%
Payment Probability	0.00%	0.00%
Minimum | Securities — AFS
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	0.00%	0.00%
Prepayment Rate	2.10%	3.20%
Default Rate	0.00%	0.00%
Loss Severity	0.30%	1.00%
Minimum | Securities carried at fair value with changes recorded in net income
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate		0.00%
Prepayment Rate		6.10%
Default Rate		1.90%
Loss Severity		22.20%
Minimum | Derivative assets — non qualifying
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Borrower Rate	3.00%
Maximum | Consideration holdback liability
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate		4.00%
Payment Probability	100.00%	100.00%
Maximum | Securities — AFS
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	37.10%	96.40%
Prepayment Rate	22.30%	21.20%
Default Rate	7.30%	9.00%
Loss Severity	72.40%	79.80%
Maximum | Securities carried at fair value with changes recorded in net income
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate		34.60%
Prepayment Rate		16.20%
Default Rate		8.10%
Loss Severity		44.70%
Maximum | Derivative assets — non qualifying
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Borrower Rate	4.40%
Weighted Average | FDIC True-up liability
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	2.90%	3.20%
Weighted Average | Consideration holdback liability
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate		2.10%
Payment Probability	48.00%	40.90%
Weighted Average | Securities — AFS
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	4.60%	5.50%
Prepayment Rate	8.80%	8.80%
Default Rate	3.70%	3.90%
Loss Severity	35.30%	36.30%
Weighted Average | Securities carried at fair value with changes recorded in net income
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount Rate	31.10%	5.60%
Prepayment Rate	10.90%	11.90%
Default Rate	2.40%	4.60%
Loss Severity	59.20%	25.80%
Weighted Average | Derivative assets — non qualifying
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Borrower Rate	3.80%