Quarterly report pursuant to Section 13 or 15(d)

Summary of Marketable Securities (Detail)

v3.8.0.1
Summary of Marketable Securities (Detail) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Schedule of Marketable Securities [Line Items]    
Trading Securities, Short-term Investments, Amortized Cost $ 77 $ 152
Trading Securities, Gross Unrealized Gain 0 16
Trading Securities, Gross Unrealized Loss 0 0
Trading Securities 77 168
Available-for-sale Securities, Amortized Cost Basis 594 584
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 1 1
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax (7) (4)
Available-for-sale Securities, Current 588 581
Total Amortized Cost 671 736
Marketable Securities, Gross Unrealized Gain 1 17
Marketable Securities, Gross Unrealized Loss (7) (4)
Total Estimated Fair Value 665 749
Corporate debt securities    
Schedule of Marketable Securities [Line Items]    
Trading Securities, Short-term Investments, Amortized Cost 75 75
Trading Securities, Gross Unrealized Gain 0 0
Trading Securities, Gross Unrealized Loss 0 0
Trading Securities 75 75
Available-for-sale Securities, Amortized Cost Basis 229 201
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 1 1
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax (2) (1)
Available-for-sale Securities, Current 228 201
Carbon credit investments    
Schedule of Marketable Securities [Line Items]    
Trading Securities, Short-term Investments, Amortized Cost   77
Trading Securities, Gross Unrealized Gain   16
Trading Securities, Gross Unrealized Loss   0
Trading Securities   93
U.S. government and agency debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 312 286
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax (4) (3)
Available-for-sale Securities, Current 308 283
Mortgage and asset-backed debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 32 86
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 0 0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax (1) 0
Available-for-sale Securities, Current 31 86
U.S. state and local municipal debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 10  
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 10  
Equity securities    
Schedule of Marketable Securities [Line Items]    
Trading Securities, Short-term Investments, Amortized Cost 2  
Trading Securities, Gross Unrealized Gain 0  
Trading Securities, Gross Unrealized Loss 0  
Trading Securities 2  
Available-for-sale Securities, Amortized Cost Basis   2
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   2
Non-U.S. government debt securities    
Schedule of Marketable Securities [Line Items]    
Available-for-sale Securities, Amortized Cost Basis 11 9
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 $ 11 $ 9