Segment Information - Financial Data by Operating Segment (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net income (losses)	$ 32	$ (106)
Midstream Segment \| Operating Segments
Segment Reporting Information [Line Items]
Net income (losses)	37	28
Midstream Segment \| Operating Segments \| Pro Forma
Segment Reporting Information [Line Items]
Net income (losses)		37
Exploration and Production \| Operating Segments
Segment Reporting Information [Line Items]
Net income (losses)	$ 109	(25)
Exploration and Production \| Operating Segments \| Pro Forma
Segment Reporting Information [Line Items]
Net income (losses)		$ (34)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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