Supplementary information (Tables)

6 Months Ended

Jun. 30, 2017

Oil and Gas Exploration and Production Industries Disclosures [Abstract]

Capitalized costs

Capitalized costs

			June 30,		December 31,
(in millions)			2017		2016
Oil and natural gas properties:
	Proved		$	17,364	$	16,620
	Unproved			2,346		1,856
	Less: accumulated depletion			(7,904)		(7,390)
		Net capitalized costs for oil and natural gas properties	$	11,806	$	11,086

costs incurred for oil and natural gas producing activities

Costs incurred for oil and natural gas producing activities

		Three Months Ended				Six Months Ended
		June 30,				June 30,
(in millions)		2017		2016		2017		2016
Property acquisition costs:
	Proved	$	12	$	4	$	139	$	256
	Unproved		87		19		393		158
Exploration			238		165		473		336
Development			145		107		303		190
	Total costs incurred for oil and natural gas properties	$	482	$	295	$	1,308	$	940