Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligations [Abstract]

Schedule of Asset Retirement Obligations

(in millions)	2017		2016
Asset retirement obligation at January 1	$	141	$	201
Accretion of discount		8		10
Obligations incurred		3		1
Obligations settled/removed (1)		(10)		(45)
Revisions of estimates		23		(26)
Asset retirement obligation at December 31	$	165	$	141
Current liability		12		6
Long-term liability		153		135
Asset retirement obligation at December 31	$	165	$	141

(1) Obligations settled/removed include $35 million related to asset divestitures in 2016.