Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2019

Asset Retirement Obligation Disclosure [Abstract]

Schedule of asset retirement obligations

The components of the change in our asset retirement obligations are shown below:

	Years Ended December 31,
	2019		2018
	($ in millions)
Asset retirement obligations, beginning of period	$	166	$	177
Additions(a)	21		3
Revisions	18		11
Settlements and disposals	(5)		(35)
Accretion expense	11		10
Asset retirement obligations, end of period	211		166
Less current portion	11		11
Asset retirement obligation, long-term	$	200	$	155

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(a)    During 2019, approximately $17 million of additions relate to the acquisition of WildHorse.