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, 2012
Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 1,169 $ 1,475
Marketable securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 947 1,241
Marketable securities | U.S. government and agency debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 216 187
Marketable securities | Mortgage and asset-backed debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 178 191
Marketable securities | Corporate debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 386 837
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 152 11
Other Long-term Investments
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 222 234
Fair Value, Inputs, Level 1
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 234 204
Fair Value, Inputs, Level 1 | Marketable securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 216 187
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 216 187
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 18 17
Fair Value, Inputs, Level 2
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 731 1,054
Fair Value, Inputs, Level 2 | Marketable securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 731 1,054
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 0 0
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 178 191
Fair Value, Inputs, Level 2 | Marketable securities | Corporate debt securities
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 386 837
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 152 11
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 204 217
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 $ 204 $ 217