Quarterly report pursuant to Section 13 or 15(d)

Summary of Marketable Securities (Detail)

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Summary of Marketable Securities (Detail) - USD ($)
$ in Millions
Sep. 30, 2017
Dec. 31, 2016
Schedule of Marketable Securities [Line Items]    
Trading Securities, Short-term Investments, Amortized Cost $ 400 $ 507
Trading Securities, Gross Unrealized Gain 46 10
Trading Securities, Gross Unrealized Loss 0 0
Trading Securities 446 517
Available-for-sale Securities, Amortized Cost Basis 597 576
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 1 1
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax (1) (3)
Available-for-sale Securities, Current 597 574
Total Amortized Cost 997 1,083
Marketable Securities, Gross Unrealized Gain 47 11
Marketable Securities, Gross Unrealized Loss (1) (3)
Total Estimated Fair Value 1,043 1,091
Corporate debt securities    
Schedule of Marketable Securities [Line Items]    
Trading Securities, Short-term Investments, Amortized Cost 159 427
Trading Securities, Gross Unrealized Gain 0 0
Trading Securities, Gross Unrealized Loss 0 0
Trading Securities 159 427
Available-for-sale Securities, Amortized Cost Basis 210 167
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 1 0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax 0 (1)
Available-for-sale Securities, Current 211 166
Carbon credit investments    
Schedule of Marketable Securities [Line Items]    
Trading Securities, Short-term Investments, Amortized Cost 241 80
Trading Securities, Gross Unrealized Gain 46 10
Trading Securities, Gross Unrealized Loss 0 0
Trading Securities 287 90
U.S. government and agency debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 286 314
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax (1) (2)
Available-for-sale Securities, Current 285 312
Mortgage and asset-backed debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 90 90
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 0 1
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Current 90 91
U.S. state and local municipal debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 0  
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 0  
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax 0  
Available-for-sale Securities, Current 0  
Equity securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 2 2
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Current 2 2
Non-U.S. government debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 9 3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax 0 0
Available-for-sale Securities, Current $ 9 $ 3