Revenue from Contracts with Customers - Impact on Financial Statements (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues
Gathering, processing, and marketing sales	$ 382	$ 464	$ 742	$ 908
Gains (losses) on divestitures and other, net	123	297	142	1,166
Expenses
Gathering, processing, and marketing	252	355	489	705
Income tax expense (benefit)	125	(38)	251	59
Net income (loss) attributable to noncontrolling interests	(12)	81	41	124
Net income (loss) attributable to common stockholders	29	$ (415)	150	$ (733)
Assets
Net properties and equipment	28,502		28,502		$ 27,451
Other Assets	2,301		2,301		2,211
Liabilities
Other current liabilities	1,699		1,699		1,310
Deferred income taxes	2,317		2,317		2,234
Other	4,031		4,031		4,109
Equity
Total equity	11,495		11,495		$ 13,790
Accounting Standards Update 2014-09 [Member] | Without Adoption of Topic 606 [Member]
Revenues
Gathering, processing, and marketing sales	650		1,227
Gains (losses) on divestitures and other, net	123		144
Expenses
Gathering, processing, and marketing	518		969
Income tax expense (benefit)	126		253
Net income (loss) attributable to noncontrolling interests	(14)		40
Net income (loss) attributable to common stockholders	32		156
Assets
Net properties and equipment	28,454		28,454
Other Assets	2,289		2,289
Liabilities
Other current liabilities	1,692		1,692
Deferred income taxes	2,325		2,325
Other	3,918		3,918
Equity
Total equity	11,547		11,547
Accounting Standards Update 2014-09 [Member] | Effect of Change Increase/ (Decrease) [Member]
Revenues
Gathering, processing, and marketing sales	(268)		(485)
Gains (losses) on divestitures and other, net	0		(2)
Expenses
Gathering, processing, and marketing	(266)		(480)
Income tax expense (benefit)	(1)		(2)
Net income (loss) attributable to noncontrolling interests	2		1
Net income (loss) attributable to common stockholders	(3)		(6)
Assets
Net properties and equipment	48		48
Other Assets	12		12
Liabilities
Other current liabilities	7		7
Deferred income taxes	(8)		(8)
Other	113		113
Equity
Total equity	$ (52)		$ (52)