Suspended Exploratory Well Costs (Tables)

12 Months Ended

Dec. 31, 2017

Capitalized Exploratory Well Costs [Abstract]

Suspended Exploratory Well Costs Rollforward

The following summarizes the changes in suspended exploratory well costs at December 31 for each of the last three years. Additions pending the determination of proved reserves excludes amounts capitalized and subsequently charged to expense within the same year:

millions	2017			2016			2015
Balance at January 1	$	1,230		$	1,124		$	1,522
Additions pending the determination of proved reserves	349			490			461
Divestitures and other	(36		)	(11		)	(33		)
Reclassifications to proved properties	(41		)	(50		)	(104		)
Charges to exploration expense	(977		)	(323		)	(722		)
Balance at December 31	$	525		$	1,230		$	1,124

Schedule of Aging of Capitalized Exploratory Well Costs

The following provides an aging of suspended well balances at December 31:

millions	2017		2016		2015
Exploratory well costs capitalized for a period of one year or less	$	201	$	460	$	452
Exploratory well costs capitalized for a period greater than one year	324		770		672
Balance at December 31	$	525	$	1,230	$	1,124

The following summarizes a further aging by geographic area of those exploratory well costs that have been capitalized for a period greater than one year since the completion of drilling at December 31, 2017:

millions except projects	Number of Projects	Total		2016		2015		2014 and prior
U.S. Onshore	9	$	44	$	10	$	4	$	30
U.S. Offshore	1	74		74		—		—
International	3	206		14		87		105
	13	$	324	$	98	$	91	$	135