Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2020

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,
	2020		2019
	($ in millions)
Asset retirement obligations, beginning of period	$	211	$	166
Additions(a)	1		21
Revisions	(14)		18
Settlements and disposals(b)	(66)		(5)
Accretion expense	12		11
Asset retirement obligations, end of period	144		211
Less current portion	5		11
Asset retirement obligation, long-term	$	139	$	200

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

(b)    During 2020, approximately $49 million and $14 million of disposals related to our Mid-Continent and Haynesville assets, respectively. See Note 3 for further discussion of these transactions.