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
Sep. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 1,070 $ 1,122
Marketable securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 1,043 1,091
Marketable securities | U.S. government and agency debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 285 312
Marketable securities | Mortgage and asset-backed debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 90 91
Marketable securities | Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 370 593
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 9 3
Marketable securities | Carbon credit investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 287 90
Other Non-Current Investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 27 31
Quoted Prices in Active Markets for Identical Assets (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 612 420
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 593 402
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 285 312
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 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 21 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 287 90
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 18
Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 450 689
Significant Other Observable Inputs (Level 2) | Marketable securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 450 689
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 90 91
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 349 593
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 9 3
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 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 8 13
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 | 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 0
Significant Unobservable Inputs (Level 3) | Other Non-Current Investments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 8 $ 13