Variable Interest Entities - Financial Data of WGP (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Statement of Operations Data
Total revenues and other		$ 3,045	$ 3,767
Operating income (loss)		551	(100)
Net Income (Loss)		174	(275)
Statement of Cash Flow Data
Net cash provided by (used in) operating activities		1,430	1,123
Net cash provided by (used in) investing activities		(1,113)	1,723
Net cash provided by (used in) financing activities		(1,507)	(198)
Balance Sheet Data
Cash and cash equivalents		3,361		$ 4,553
Net properties and equipment related to VIEs		27,758		27,451
Total assets		41,076		42,086
Long-term debt		15,643		15,547
Total equity		11,756		13,790
Variable Interest Entity, Primary Beneficiary [Member]
Balance Sheet Data
Cash and cash equivalents		524		80
Net properties and equipment related to VIEs		6,064		5,731
WGP [Member]
Balance Sheet Data
Long-term debt	[1]	0		28
WGP [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Statement of Operations Data
Total revenues and other		437	516
Operating income (loss)		187	138
Net Income (Loss)		150	103
Statement of Cash Flow Data
Net cash provided by (used in) operating activities		241	192
Net cash provided by (used in) investing activities		(294)	(252)
Net cash provided by (used in) financing activities		497	$ (176)
Balance Sheet Data
Cash and cash equivalents		524		80
Net properties and equipment related to VIEs		6,064		5,731
Total assets		8,816		8,016
Long-term debt		4,176		3,493
Total liabilities		4,967		4,071
Total equity		$ 3,849		$ 3,945

[1] Excludes WES.