Fair Value (Changes in Estimated Fair Value for Financial Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Derivative Liabilities - Non Qualifying [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (11.5)	$ (55.5)
Included in earnings, liability	1.2	(26.8)
Included in comprehensive income, liability	0.0	0.0
Impairment, liability	0.0	0.0
Settlements, liability	0.0	0.0
Ending Balance	(12.7)	(28.7)
FDIC True-Up Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(61.9)	(56.9)
Included in earnings, liability	2.4	2.8
Included in comprehensive income, liability	0.0	0.0
Impairment, liability	0.0	0.0
Settlements, liability	0.0	0.0
Ending Balance	(64.3)	(59.7)
Consideration Holdback Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(47.2)	(60.8)
Included in earnings, liability	(1.1)	0.7
Included in comprehensive income, liability	0.0	0.0
Impairment, liability	0.0	0.0
Settlements, liability	0.0	14.3
Ending Balance	(46.1)	(47.2)
Available-For-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	485.5	567.1
Included in earnings, assets	(2.9)	(3.1)
Included in comprehensive income, assets	14.0	12.5
Impairment, assets	(0.1)	(2.2)
Settlements, assets	(39.7)	(50.9)
Ending Balance	456.8	523.4
Securities Carried At Fair Value With Changed Recorded In Net Income [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	283.5	339.7
Included in earnings, assets	8.0	5.5
Included in comprehensive income, assets	0.0	0.0
Impairment, assets	0.0	0.0
Settlements, assets	(35.9)	(32.6)
Ending Balance	255.6	312.6
FDIC Receivable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0.6	54.8
Included in earnings, assets	0.7	5.0
Included in comprehensive income, assets	0.0	0.0
Impairment, assets	0.0	0.0
Settlements, assets	0.0	(6.6)
Ending Balance	1.3	53.2
Derivative Assets - Non Qualifying [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0.0	0.0
Included in earnings, assets	0.1	0.2
Included in comprehensive income, assets	0.0	0.0
Impairment, assets	0.0	0.0
Settlements, assets	0.0	0.0
Ending Balance	$ 0.1	$ 0.2