Fair Value (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities AFS	$ 6,123.6
Securities carried at fair value with changes recorded in net income	0.4	$ 283.5
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities AFS	6,123.6	3,674.1
Securities carried at fair value with changes recorded in net income	0.4	283.5
Equity Securities AFS	44.7	34.1
Total Assets	6,237.4	4,103.3
Consideration holdback liability	(46.0)	(47.2)
FDIC True-up Liability	(65.1)	(61.9)
Total Liabilities	(198.1)	(177.9)
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities AFS	199.0	200.1
Securities carried at fair value with changes recorded in net income	0.0	0.0
Equity Securities AFS	0.2	0.3
Total Assets	199.2	200.4
Consideration holdback liability	0.0	0.0
FDIC True-up Liability	0.0	0.0
Total Liabilities	0.0	0.0
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities AFS	5,538.8	2,988.5
Securities carried at fair value with changes recorded in net income	0.0	0.0
Equity Securities AFS	44.5	33.8
Total Assets	5,651.9	3,133.9
Consideration holdback liability	0.0	0.0
FDIC True-up Liability	0.0	0.0
Total Liabilities	(72.9)	(57.3)
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities AFS	385.8	485.5
Securities carried at fair value with changes recorded in net income	0.4	283.5
Equity Securities AFS	0.0	0.0
Total Assets	386.3	769.0
Consideration holdback liability	(46.0)	(47.2)
FDIC True-up Liability	(65.1)	(61.9)
Total Liabilities	(125.2)	(120.6)
Non-Qualifying Hedges | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	68.5	94.7
Derivative liabilities at fair value	(68.3)	(68.8)
Non-Qualifying Hedges | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	0.0	0.0
Derivative liabilities at fair value	0.0	0.0
Non-Qualifying Hedges | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	68.4	94.7
Derivative liabilities at fair value	(54.2)	(57.3)
Non-Qualifying Hedges | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	0.1	0.0
Derivative liabilities at fair value	(14.1)	(11.5)
Qualifying Hedges | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	0.2	16.9
Derivative liabilities at fair value	(18.7)
Qualifying Hedges | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	0.0	0.0
Qualifying Hedges | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	0.2	16.9
Derivative liabilities at fair value	(18.7)
Qualifying Hedges | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets at fair value	$ 0.0	$ 0.0