Exploratory well costs (Tables)

6 Months Ended

Jun. 30, 2017

Disclosure Exploratory Well Costs Capitalized Exploratory Well Activity [Abstract]

Company's capitalized exploratory well activity

The following table reflects the Company’s net capitalized exploratory well activity during the six months ended June 30,2017:

		Six Months Ended
(in millions)		June 30, 2017
Beginning capitalized exploratory well costs		$	151
	Additions to exploratory well costs pending the determination of proved reserves		268
	Reclassifications due to determination of proved reserves		(126)
Ending capitalized exploratory well costs		$	293

Aging of capitalized exploratory well costs based on the date drilling was completed

The following table provides an aging at June 30,2017 and December 31, 2016 of capitalized exploratory well costs based on the date drilling was completed:

			June 30,		December 31,
(dollars in millions)			2017		2016
Capitalized exploratory well costs that have been capitalized for a period of one year or less		$	288	$	141
Capitalized exploratory well costs that have been capitalized for a period greater than one year			5		10
	Total capitalized exploratory well costs	$	293	$	151
Number of projects with exploratory well costs that have been capitalized for a period greater
	than one year		6		8