Asset Retirement Obligations (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Changes to the asset retirement obligations
Beginning Balance		$ 812	$ 570
Changes in timing and amount of estimated cash flows			203
Liabilities settled		(2)	(1)
Accretion		46	40
Ending Balance	$ 812	856	812
Noncurrent liabilities - held for sale (Note 10)	0	691	$ 0
TMI-2
Changes to the asset retirement obligations
Noncurrent liabilities - held for sale (Note 10)		$ 691
Increase in asset retirement obligation	$ 172

Asset Retirement Obligation Period Increase Decrease.

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- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Amount of increase (decrease) in asset retirement obligations.

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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Amount classified as liabilities attributable to disposal group held for sale or disposed of, expected to be disposed of beyond one year or the normal operating cycle, if longer.

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