Variable Interest Entities (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Variable Interest Entity [Line Items]
Interest income for WES	$ 259	$ 244	$ 517	$ 498
Variable Interest Entity, Primary Beneficiary [Member] | Western Gas Partners, LP [Member]
Variable Interest Entity [Line Items]
Note receivable for WES	$ 260		$ 260
Debt instrument, term			30 years
Fixed annual rate	6.50%		6.50%
Interest income for WES	$ 4	$ 4	$ 8	8
Deferred purchase price obligation - Anadarko	$ 29		29		$ 189
Above-market component of swap extensions with Anadarko			$ 16	$ 0