Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 620.8	$ 599.2	$ 1,923.8	$ 1,672.8
Interest Expense	203.1	191.0	666.7	467.3
Other Operating Income	45.1	20.9	113.0	87.1
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	2.8	3.5	13.3	6.4
Gains/(Losses) on cash flow hedges recognized on	2.6	17.2	20.3	47.3
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	(6.0)	(6.4)	(3.9)	3.3
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	1.4	0.2	1.1	3.7
Foreign Exchange Contracts \| Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	2.7	17.3	20.8	47.5
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	1.4	0.2	1.1	3.7
Interest Rate Contracts \| Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(14.9)	13.0	(99.0)	77.7
Recognized on hedged items	14.9	(13.0)	99.0	(77.7)
Amounts related to interest settlements on derivatives	2.8	3.5	13.3	6.4
Gains/(Losses) on cash flow hedges recognized on	(0.1)	(0.1)	(0.5)	(0.2)
Interest Rate Contracts \| Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	51.4	(8.9)	141.6	(46.0)
Recognized on hedged items	(51.4)	8.9	(141.6)	46.0
Amounts related to interest settlements on derivatives	(6.0)	(6.4)	(3.9)	3.3
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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