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Risk Management and Financial Instruments - Financial Instruments Measured at Fair Value on a Recurring Basis (Detail) - USD ($)
$ in Millions
Jun. 30, 2018
Dec. 31, 2017
Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities-current asset $ 121 $ 124
Interest rate cap - current asset 61  
Convertible debt instrument-non-current asset 58 52
Total assets 240 176
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities-current asset 121 124
Total assets 121 124
Fair Value Measurements as at the Reporting Date Using Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Interest rate cap - current asset 61  
Total assets 61  
Significant Unobservable Inputs (Level 3) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Convertible debt instrument-non-current asset 58 52
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Convertible debt instrument-non-current asset 58 52
Total assets $ 58 $ 52