Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 567.7	$ 417.2	$ 1,073.6	$ 827.5
Interest Expense	154.4	75.7	276.3	132.5
Other Operating Income	31.4	43.0	66.2	82.7
Other Operating Expense	75.3	82.3	144.3	147.4
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	6.6	1.5	2.9	(4.8)
Gains/(Losses) on cash flow hedges recognized on	15.9	3.6	30.1	8.1
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	8.3	15.2	9.7	17.2
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0	0.0	0.0
Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	0.0	0.0	0.0	0.0
Gains/(Losses) on cash flow hedges recognized on	1.1	1.8	3.5	2.5
Other Operating Expense
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	0.0	0.0	0.0	0.0
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0	0.0	(0.1)
Foreign Exchange Contracts | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	16.0	3.5	30.2	7.9
Foreign Exchange Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0	0.0	0.0
Foreign Exchange Contracts | Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	1.1	1.8	3.5	2.5
Foreign Exchange Contracts | Other Operating Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0	0.0	(0.1)
Interest Rate Contracts | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	10.4	(24.6)	64.7	(20.8)
Recognized on hedged items	(10.4)	24.6	(64.7)	20.8
Amounts related to interest settlements on derivatives	6.6	1.5	2.9	(4.8)
Gains/(Losses) on cash flow hedges recognized on	(0.1)	0.1	(0.1)	0.2
Interest Rate Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(15.2)	(5.3)	(37.1)	(4.1)
Recognized on hedged items	15.2	5.3	37.1	4.1
Amounts related to interest settlements on derivatives	8.3	15.2	9.7	17.2
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0	0.0	0.0
Interest Rate Contracts | Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0.0	0.0	0.0	0.0
Recognized on hedged items	0.0	0.0	0.0	0.0
Amounts related to interest settlements on derivatives	0.0	0.0	0.0	0.0
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0	0.0	0.0
Interest Rate Contracts | Other Operating Expense
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0.0	0.0	0.0	0.0
Recognized on hedged items	0.0	0.0	0.0	0.0
Amounts related to interest settlements on derivatives	0.0	0.0	0.0	0.0
Gains/(Losses) on cash flow hedges recognized on	$ 0.0	$ 0.0	$ 0.0	$ 0.0