v2.4.0.6
Derivative Instruments (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Interest Rate Contract [Member]
   
Derivative [Line Items]    
Notional amount of interest rate derivative purchase contracts $ 434.1 $ 377.8
Notional amount of interest rate derivative sale contracts 317.6 310.7
Foreign Currency Forward Contracts, Underwriting and Non-investment Operations [Member]
   
Derivative [Line Items]    
Notional amount of foreign currency derivative purchase contracts 417.4 446.2
Notional amount of foreign currency derivative sale contracts 230.6 119.5
Foreign Currency Forward Contracts, Investment Operations [Member]
   
Derivative [Line Items]    
Notional amount of foreign currency derivative purchase contracts 275.2 176.7
Notional amount of foreign currency derivative sale contracts 314.9 217.4
Foreign Currency Forward Contracts, Energy And Risk Operations [Member]
   
Derivative [Line Items]    
Notional amount of foreign currency derivative purchase contracts 0 0
Notional amount of foreign currency derivative sale contracts 47.4 38.2
Credit Risk Contract [Member]
   
Derivative [Line Items]    
Notional amount of credit risk derivative purchase contracts 4.7 46.1
Notional amount of credit risk derivative sale contracts $ 27.2 $ 24.0