Derivative Financial Instruments (Location and Amount of Derivative Gains and Losses Recorded in Income) (Details) - Asset And Liability Management - Fair Value Hedges - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain Recognized in Income	$ (13.2)	$ (1.7)	$ (12.5)	$ 11.1
Available for Sale Investment Securities | Interest Rate Swap Contracts | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain Recognized in Income	(23.1)	(25.2)	(25.6)	(59.9)
Senior Notes and Long-Term Subordinated Debt | Interest Rate Swap Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain Recognized in Income	$ 9.9	$ 23.5	$ 13.1	$ 71.0