Segment Information - Schedule of Identifiable Assets by Operating Segment (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Identifiable assets	$ 35,558	$ 38,578
Continuing Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	35,487	37,420
Continuing Operations [Member] | Exploration and Production [Member]
Segment Reporting Information [Line Items]
Identifiable assets	31,992	32,742
Continuing Operations [Member] | Bakken Midstream [Member]
Segment Reporting Information [Line Items]
Identifiable assets	2,550	2,465
Continuing Operations [Member] | Corporate, Interest and Other [Member]
Segment Reporting Information [Line Items]
Identifiable assets	945	2,213
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	$ 71	$ 1,158