Fair Value Measurements - Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions		Mar. 31, 2017		Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash collateral netted with derivative liabilities		$ 28		$ 24
Contingent consideration, current		131		130
Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Embedded derivatives, current		6		13
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - netting and collateral		(391)		(688)
Commodity derivative instruments, assets - collateral pledged not offset		78		126
Other assets		2		2
Total assets at fair value		3		2
Commodity derivative instruments, liabilities - netting and collateral		(419)		(712)
Commodity derivative instruments, liabilities - collateral pledged not offset		0		0
Contingent consideration, liability		131		130
Total liabilities at fair value		174		190
Fair Value, Measurements, Recurring | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - netting and collateral	[1]	(391)		(688)
Commodity derivative instruments, assets - net carrying value on balance sheet	[2]	1		0
Commodity derivative instruments, assets - collateral pledged not offset		78		126
Commodity derivative instruments, liabilities - netting and collateral	[1]	(419)		(712)
Commodity derivative instruments, liabilities - net carrying value on balance sheet	[2]	(1)		6
Commodity derivative instruments, liabilities - collateral pledged not offset		0		0
Fair Value, Measurements, Recurring | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - netting and collateral		0		0
Commodity derivative instruments, liabilities - net carrying value on balance sheet	[2]	44		54
Commodity derivative instruments, liabilities - collateral pledged not offset		0		0
Fair Value, Measurements, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets		2		2
Total assets at fair value		392		690
Contingent consideration, liability		0		0
Total liabilities at fair value		416		712
Fair Value, Measurements, Recurring | Level 1 | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross		390		688
Commodity derivative instruments, liabilities - gross		416		712
Fair Value, Measurements, Recurring | Level 1 | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross		0		0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets		0		0
Total assets at fair value		0		0
Contingent consideration, liability		0		0
Total liabilities at fair value		0		0
Fair Value, Measurements, Recurring | Level 2 | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross		0		0
Commodity derivative instruments, liabilities - gross		0		0
Fair Value, Measurements, Recurring | Level 2 | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross		0		0
Fair Value, Measurements, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets		0		0
Total assets at fair value		2		0
Contingent consideration, liability	[3]	131		130
Total liabilities at fair value		177		190
Fair Value, Measurements, Recurring | Level 3 | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross		2		0
Commodity derivative instruments, liabilities - gross		2	[4]	6
Fair Value, Measurements, Recurring | Level 3 | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross	[4]	$ 44		$ 54

[1] Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of March 31, 2017, cash collateral of $28 million was netted with the mark-to-market derivative liabilities. As of December 31, 2016, $24 million was netted with mark-to-market derivative liabilities.

[2] We have no derivative contracts which are subject to master netting arrangements reflected gross on the balance sheet.

[3] Includes $131 million and $130 million classified as current at March 31, 2017 and December 31, 2016, respectively.

[4] ncludes $6 million and $13 million classified as current at March 31, 2017 and December 31, 2016, respectively.