Debt and Interest Expense - Scheduled Maturities Table (Detail) $ in Millions	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
2018	$ 481
2019	928
2020	370
2021	1,300
2022	670
Western Gas Partners, LP [Member]
Debt Instrument [Line Items]
2018	350
2019	0
2020	370
2021	500
2022	670
Western Gas Equity Partners, LP excluding WES [Member]
Debt Instrument [Line Items]
2018	0	[1]
2019	28	[1]
2020	0	[1]
2021	0	[1]
2022	0	[1]
Anadarko Excluding WES and WGP [Member]
Debt Instrument [Line Items]
2018	131	[2]
2019	900	[2]
2020	0	[2]
2021	800	[2]
2022	$ 0	[2]

[1] Excludes WES.

[2] Excludes WES and WGP