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
Mar. 31, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 687 $ 774
Marketable securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 665 749
Marketable securities | U.S. government and agency debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 308 283
Marketable securities | Mortgage and asset-backed debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 31 86
Marketable securities | Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 303 276
Marketable securities | U.S. state and local municipal debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 10  
Marketable securities | Equity securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 2 2
Marketable securities | Non-U.S. government debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 11 9
Marketable securities | Carbon credit investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments   93
Other Non-Current Investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 22 25
Quoted Prices in Active Markets for Identical Assets (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 327 395
Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 308 376
Quoted Prices in Active Markets for Identical Assets (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 308 283
Quoted Prices in Active Markets for Identical Assets (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
Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable securities | Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Quoted Prices in Active Markets for Identical Assets (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  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable securities | Equity securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable securities | Non-U.S. government debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable securities | Carbon credit investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments   93
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Non-Current Investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 19 19
Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 357 373
Significant Other Observable Inputs (Level 2) | Marketable securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 357 373
Significant Other Observable 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
Significant Other Observable 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 31 86
Significant Other Observable Inputs (Level 2) | Marketable securities | Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 303 276
Significant Other Observable 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 10  
Significant Other Observable Inputs (Level 2) | Marketable securities | Equity securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 2 2
Significant Other Observable Inputs (Level 2) | Marketable securities | Non-U.S. government debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 11 9
Significant Other Observable Inputs (Level 2) | Marketable securities | Carbon credit investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments   0
Significant Other Observable Inputs (Level 2) | Other Non-Current Investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 3 6
Significant Unobservable Inputs (Level 3) | Marketable securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Significant Unobservable 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
Significant Unobservable 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
Significant Unobservable Inputs (Level 3) | Marketable securities | Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Significant Unobservable 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  
Significant Unobservable Inputs (Level 3) | Marketable securities | Equity securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Significant Unobservable Inputs (Level 3) | Marketable securities | Non-U.S. government debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 0 0
Significant Unobservable Inputs (Level 3) | Marketable securities | Carbon credit investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments   0
Significant Unobservable Inputs (Level 3) | Other Non-Current Investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 3 $ 6