Quarterly report pursuant to Section 13 or 15(d)

Investments Measured at Fair Value on a Recurring Basis (Detail)

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Investments Measured at Fair Value on a Recurring Basis (Detail) (Fair Value, Measurements, Recurring [Member], USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 1,045 $ 779
Marketable securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 876 597
Marketable securities | U.S. government and agency debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 241 238
Marketable securities | Mortgage and asset-backed debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 143 174
Marketable securities | Corporate debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 421 163
Marketable securities | U.S. state and local municipal debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 15 15
Marketable securities | Other debt and equity securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 56 7
Other Long-term Investments
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 169 182
Fair Value, Inputs, Level 1
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 259 256
Fair Value, Inputs, Level 1 | Marketable securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 240 237
Fair Value, Inputs, Level 1 | Marketable securities | U.S. government and agency debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 240 237
Fair Value, Inputs, Level 1 | Marketable securities | Mortgage and asset-backed debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 1 | Marketable securities | Corporate debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 1 | Marketable securities | U.S. state and local municipal debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 1 | Marketable securities | Other debt and equity securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 1 | Other Long-term Investments
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 19 19
Fair Value, Inputs, Level 2
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 636 360
Fair Value, Inputs, Level 2 | Marketable securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 636 360
Fair Value, Inputs, Level 2 | Marketable securities | U.S. government and agency debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 1 1
Fair Value, Inputs, Level 2 | Marketable securities | Mortgage and asset-backed debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 143 174
Fair Value, Inputs, Level 2 | Marketable securities | Corporate debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 421 163
Fair Value, Inputs, Level 2 | Marketable securities | U.S. state and local municipal debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 15 15
Fair Value, Inputs, Level 2 | Marketable securities | Other debt and equity securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 56 7
Fair Value, Inputs, Level 2 | Other Long-term Investments
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 3
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 150 163
Fair Value, Inputs, Level 3 | Marketable securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 3 | Marketable securities | U.S. government and agency debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 3 | Marketable securities | Mortgage and asset-backed debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 3 | Marketable securities | Corporate debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 3 | Marketable securities | U.S. state and local municipal debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 3 | Marketable securities | Other debt and equity securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Fair Value, Inputs, Level 3 | Other Long-term Investments
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 150 $ 163