Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income for Derivatives Not Designated As Hedging Under GAAP) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Derivatives Not Designated as Hedging under GAAP
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 53.6	$ 56.8
Non-Designated Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	(5.6)	(1.4)
Non-Designated Risk Management Derivatives \| Foreign Exchange Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 0.0	$ (0.2)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Operating Income	Other Operating Income
Non-Designated Risk Management Derivatives \| Other Financial Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ (5.6)	$ (1.2)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Operating Income	Other Operating Income
Client-Related and Trading Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 59.2	$ 58.2
Client-Related and Trading Derivatives \| Foreign Exchange Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 58.7	$ 57.0
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Foreign Exchange Trading Income	Foreign Exchange Trading Income
Client-Related and Trading Derivatives \| Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 0.5	$ 1.2
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Security Commissions and Trading Income	Security Commissions and Trading Income

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

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Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative.

+ References

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4E

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