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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ 8.2	$ 21.2	$ 19.4	$ 11.0
Securities Available for Sale | Interest Rate Swap Contracts | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	15.5	(22.5)	(44.3)	(34.8)
Senior Notes and Long-Term Subordinated Debt | Interest Rate Swap Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of derivative gain/(loss) recognized in income	$ (7.3)	$ 43.7	$ 63.7	$ 45.8