Derivative Financial Instruments (Gains (Losses) of Non-Qualifying Hedges Recognized as Other Non-interest Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges - income statement impact	$ 8.5	$ 13.5
Non-Qualifying Hedges | Interest rate contracts | Other Non-Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges - income statement impact		0.1
Non-Qualifying Hedges | Foreign currency forward contracts | Other Non-Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges - income statement impact	10.9	13.3
Non-Qualifying Hedges | Other contracts | Other Non-Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Non-qualifying hedges - income statement impact	$ (2.4)	$ 0.1