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Fair Value of Financial Investments and Liabilities - Changes in Level 3 Financial Assets Measured at Fair Value on Recurring Basis (Detail) (Auction Rate Securities [Member], USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Auction Rate Securities [Member]
   
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value at beginning of period $ 22 $ 22
Total losses included in earnings      
Unrealized (losses)      
Purchases      
Settlements      
Transfer from Level 3 to Level 2      
Fair value at period end $ 22 $ 22