Oil and Gas Properties (Tables)

12 Months Ended

Dec. 31, 2016

Oil and Gas Property [Abstract]

Costs incurred by year for oil and gas properties not subject to amortization

Costs withheld from amortization as of December 31, 2016 consisted of the following:

	Costs Incurred In
	2016		2015		2014		2013		Total
	(In millions)
Acquisition costs	$	540	$	339	$	162	$	74	$	1,115
Exploration costs	4		—		—		—		4
Capitalized interest	51		33		35		—		119
Total costs withheld from amortization (unproved)	$	595	$	372	$	197	$	74	$	1,238

Capitalized Costs Relating to Oil and Gas Producing Activities and Other PPE [Table Text Block]

At December 31, oil and gas properties consisted of the following:

	2016			2015
	(In millions)
Proved	$	21,998		$	21,568
Unproved	1,238			780
Gross oil and gas properties	23,236			22,348
Accumulated depreciation, depletion and amortization	(9,587		)	(9,048		)
Accumulated impairment	(10,509		)	(9,481		)
Net oil and gas properties	$	3,140		$	3,819