v3.25.2
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 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Derivatives Not Designated as Hedging under GAAP        
Derivative Instruments, Gain (Loss) [Line Items]        
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME $ 52.0 $ 43.7 $ 105.6 $ 100.5
Non-Designated Risk Management Derivatives        
Derivative Instruments, Gain (Loss) [Line Items]        
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME 0.2 (15.4) (5.4) (16.8)
Non-Designated Risk Management Derivatives | Foreign Exchange Contracts        
Derivative Instruments, Gain (Loss) [Line Items]        
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME $ 0.0 $ 0.0 $ 0.0 $ (0.2)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Other Operating Income Other Operating Income 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 $ 0.2 $ (15.4) $ (5.4) $ (16.6)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Other Operating Income Other Operating Income 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 $ 51.8 $ 59.1 $ 111.0 $ 117.3
Client-Related and Trading Derivatives | Foreign Exchange Contracts        
Derivative Instruments, Gain (Loss) [Line Items]        
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME $ 50.6 $ 58.4 $ 109.3 $ 115.4
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Foreign Exchange Trading Income Foreign Exchange Trading Income 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 $ 1.2 $ 0.7 $ 1.7 $ 1.9
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Security Commissions and Trading Income Security Commissions and Trading Income Security Commissions and Trading Income Security Commissions and Trading Income