Oil and Gas Assets (Tables)

3 Months Ended

Mar. 31, 2017

Oil and Gas Property [Abstract]

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

Costs withheld from amortization as of March 31, 2017 consisted of the following:

	Costs Incurred In
	2017		2016		2015		2014 & Prior		Total
	(In millions)
Acquisition costs	$	40	$	532	$	339	$	196	$	1,107
Exploration costs	—		2		—		—		2
Capitalized interest	16		51		33		31		131
Total costs withheld from amortization	$	56	$	585	$	372	$	227	$	1,240

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

Oil and gas properties consisted of the following:

	March 31,   2017			December 31,   2016
	(In millions)
Proved	$	22,253		$	21,998
Unproved	1,240			1,238
Gross oil and gas properties	23,493			23,236
Accumulated depreciation, depletion and amortization	(9,690		)	(9,587		)
Accumulated impairment	(10,509		)	(10,509		)
Net oil and gas properties	$	3,294		$	3,140