Impairments (Tables)

12 Months Ended

Dec. 31, 2017

Asset Impairment Charges [Abstract]

Schedule of Impairment Expense

The following summarizes impairments of long-lived assets and the related post-impairment fair values by segment at December 31:

	2017				2016				2015
millions	Impairment		Fair Value (1)		Impairment		Fair Value (1)		Impairment		Fair Value (1)
Exploration and Production
U.S. onshore properties	$	2	$	3	$	28	$	617	$	3,684	$	1,253
Gulf of Mexico properties	227		216		27		61		349		65
Cost-method investment (2)	—		—		59		—		3		59
WES Midstream	176		58		16		3		515		36
Other Midstream	2		—		57		29		524		176
Other	1		—		40		—		—		—
Total impairments	$	408	$	277	$	227	$	710	$	5,075	$	1,589

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⁽¹⁾  Measured as of the impairment date using the income approach and Level 3 inputs. The primary assumptions used to estimate undiscounted future net cash flows include anticipated future production, commodity prices, and capital and operating costs.

⁽²⁾  The after-tax net investment fair value was $32 million at December 31, 2015.