v2.4.0.6
Commitments, Contingencies and Guarantees (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Commitments and Contingencies Disclosure [Line Items]    
Financial guarantees obtained $ 13 $ 7
Voluntary accommodation program 62  
Clearinghouse Credit Facilities [Member]
    
Commitments and Contingencies Disclosure [Line Items]    
Credit facilities, total 308 310
Line of credit facility, available liquidity 216 217
Credit facility, regulatory requirements amount 92 93
Line of credit, outstanding amount 0 0
Escrow Agreement [Member]
    
Commitments and Contingencies Disclosure [Line Items]    
Contingency, accrual 18  
Property Lease Guarantee [Member]
    
Commitments and Contingencies Disclosure [Line Items]    
Other guarantees 18 18
Performance guarantees [Member]
    
Commitments and Contingencies Disclosure [Line Items]    
Other guarantees 5 5
Customer Defaults [Member]
    
Commitments and Contingencies Disclosure [Line Items]    
Other guarantees 25  
SEC Reserve Matter [Member]
    
Commitments and Contingencies Disclosure [Line Items]    
Contingency, accrual $ 10