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Financial Instruments and Risk Management - Details of Securities that Currently are in Unrealized Loss Position (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months, Fair Values    $ 79
Less than 12 months, Unrealized Losses      
More than 12 months, Fair Values 88 147
More than 12 months, Unrealized Losses (1) (6)
Total, Fair Values 88 226
Total, Unrealized Losses (1) (6)
Senior Debt Floating Rate Notes [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months, Fair Values    79
Less than 12 months, Unrealized Losses      
More than 12 months, Fair Values 88 147
More than 12 months, Unrealized Losses (1) (6)
Total, Fair Values 88 226
Total, Unrealized Losses $ (1) $ (6)