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Collateral (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Sep. 30, 2011
Settlement Guarantee Management [Abstract]    
Cash equivalents $ 886 $ 931
Pledged securities at market value 284 296
Letters of credit 966 902
Guarantees 1,996 1,845
Total $ 4,132 $ 3,974