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Changes in Level 3 Recurring Fair Value Measurements (Detail) (Notes Receivable, USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Notes Receivable
       
Fair Value Measurements [Line Items]        
Beginning of period $ 122 $ 109 $ 116 $ 103
Accretion of value (interest income) 4 3 11 9
Unrealized loss (OCI)   (2)   (2)
Other     (1)  
End of period $ 126 $ 110 $ 126 $ 110