ASSET RETIREMENT OBLIGATIONS - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 MW
Changes to the asset retirement obligations
Beginning Balance	$ 856	$ 812
Liabilities settled	(744)	(2)
Accretion	47	46
Ending Balance	159	856
Noncurrent liabilities - held for sale (Note 15)	0	691
TMI-2
Changes to the asset retirement obligations
Noncurrent liabilities - held for sale (Note 15)		$ 691
Decrease in asset retirement obligation	$ 726
Pleasants Power Station \| Purchase Agreement with Subsidiary of LS Power \| AE Supply
Asset Retirement Obligations [Line Items]
Plant generation capacity (in MW's) \| MW			1,300

Asset Retirement Obligation Period Increase Decrease.

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Asset Retirement Obligations.

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Plant Capacity

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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 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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