Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Foreign Exchange Trading Income	$ 71.7	$ 49.1	$ 229.1	$ 147.1
Treasury Management Fees	12.5	13.2	40.0	42.8
Security Commissions and Trading Income	21.9	21.2	75.2	65.8
Other operating income	20.9		87.1
Investment Security Losses, net	(0.1)	(0.4)	(0.3)	(1.1)
Total Other Noninterest Income	126.9		431.1
Noninterest Income	1,066.1	991.0	3,250.9	2,901.6
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	396.0		1,191.0
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	468.5		1,399.1
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	24.3		80.9
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	50.4		148.8
Total Trust, Investment and Other Servicing Fees
Disaggregation of Revenue [Line Items]
Revenue from contract with client	939.2	$ 867.9	2,819.8	$ 2,524.3
Other Operating Income
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 10.4		$ 33.3

Other Noninterest Income

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Revenues earned for buying and selling securities on behalf of clients and other fees including fees earned for transitioning assets between investment firms, fees earned for buying and selling interest rate protection products, and other fees.

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Fees earned from treasury management activities including disbursements and receivables management, funds transfer, and online reporting.

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Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

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Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

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The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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