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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 640.2	$ 567.7	$ 1,303.0	$ 1,073.6
Interest Expense	222.8	154.4	463.6	276.3
Other Operating Income	38.9	31.4	67.9	66.2
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	5.0	6.6	10.5	2.9
Gains/(Losses) on cash flow hedges recognized on	3.5	15.9	17.7	30.1
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	3.7	8.3	2.1	9.7
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	0.3	1.1	(0.3)	3.5
Foreign Exchange Contracts \| Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	3.7	16.0	18.1	30.2
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	0.3	1.1	(0.3)	3.5
Interest Rate Contracts \| Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(48.7)	10.4	(84.1)	64.7
Recognized on hedged items	48.7	(10.4)	84.1	(64.7)
Amounts related to interest settlements on derivatives	5.0	6.6	10.5	2.9
Gains/(Losses) on cash flow hedges recognized on	(0.2)	(0.1)	(0.4)	(0.1)
Interest Rate Contracts \| Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	61.7	(15.2)	90.2	(37.1)
Recognized on hedged items	(61.7)	15.2	(90.2)	37.1
Amounts related to interest settlements on derivatives	3.7	8.3	2.1	9.7
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

Change in Unrealized Gain (Loss) on Amounts Related to Settlement

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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