Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 662.8	$ 505.9
Interest Expense	240.8	121.9
Other Operating Income	29.0	34.8
Other Operating Expense	72.7	69.0
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	5.5	(3.7)
Gains/(Losses) on cash flow hedges recognized on	14.2	14.2
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	(1.6)	1.5
Gains/(Losses) on cash flow hedges recognized on	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
Gains/(Losses) on cash flow hedges recognized on	(0.6)	2.4
Foreign Exchange Contracts \| Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	14.4	14.2
Foreign Exchange Contracts \| Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0
Foreign Exchange Contracts \| Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	(0.6)	2.4
Interest Rate Contracts \| Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(35.4)	54.3
Recognized on hedged items	35.4	(54.3)
Amounts related to interest settlements on derivatives	5.5	(3.7)
Gains/(Losses) on cash flow hedges recognized on	(0.2)	0.0
Interest Rate Contracts \| Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	28.5	(21.9)
Recognized on hedged items	(28.5)	21.9
Amounts related to interest settlements on derivatives	(1.6)	1.5
Gains/(Losses) on cash flow hedges recognized on	0.0	0.0
Interest Rate Contracts \| Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0.0	0.0
Recognized on hedged items	0.0	0.0
Amounts related to interest settlements on derivatives	0.0	0.0
Gains/(Losses) on cash flow hedges recognized on	$ 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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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period.

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Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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