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Asset Retirement Obligations
9 Months Ended
Sep. 30, 2020
Asset Retirement Obligation [Abstract]  
Asset Retirement Obligations Asset Retirement Obligations
The changes in asset retirement obligations are as follows: 
 Nine Months Ended September 30, 2020
 (in millions)
Beginning asset retirement obligations$191 
New wells placed on production
Changes in estimates (a)(3)
Liabilities settled(30)
Accretion of discount
Ending asset retirement obligations167 
Less current portion of asset retirement obligations(32)
Asset retirement obligations - noncurrent$135 
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(a)Changes in estimates are determined based on several factors, including updating abandonment cost estimates using recent actual costs incurred to abandon wells, credit-adjusted risk-free discount rates, economic well life estimates and forecasted timing of abandoning wells.