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Marketable Securities - Additional Information (Detail)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
USD ($)
Investment
Y
Dec. 31, 2011
USD ($)
Dec. 31, 2011
EUR (€)
Dec. 31, 2010
USD ($)
Dec. 31, 2011
Debt securities issued by foreign governments [Member]
USD ($)
Dec. 31, 2010
Debt securities issued by foreign governments [Member]
USD ($)
Dec. 31, 2012
Moody's, Aaa Rating [Member]
USD ($)
Dec. 31, 2011
Moody's, Aaa Rating [Member]
USD ($)
Dec. 31, 2011
A2 by Moody's [Member]
Debt securities issued by foreign governments [Member]
USD ($)
Financing Receivable, Recorded Investment [Line Items]                  
Italian Treasury Bills $ 238 $ 413   $ 1,124 $ 81 $ 213 $ 150 $ 100 $ 81
Minimum duration of government debt securities portfolio 5 months                
Investment positions in floating-rate notes 3                
Number of Unrealized loss position in unrealized loss position 3                
Duration of the floating rate note portfolio 1                
Aggregate amortized cost basis of securities 89 252              
Pre-tax unrealized loss 1                
Senior unsecured bonds issued   5              
Original investment of senior unsecured bonds     15            
Cash proceeds from sale of senior unsecured bonds 5                
Fixed rate debt securities   $ 27