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Asset Retirement Obligations (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of December 31, 2019	$ 728
Revisions in estimates for current obligations	26
Additions	3
Spending for current obligations	(43)
Accretion	46
Balance as of December 31, 2020	760
Nuclear Decommission
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of December 31, 2019	298
Revisions in estimates for current obligations	(12)
Additions	0
Spending for current obligations	0
Accretion	17
Balance as of December 31, 2020	303
Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of December 31, 2019	430
Revisions in estimates for current obligations	38
Additions	3
Spending for current obligations	(43)
Accretion	29
Balance as of December 31, 2020	$ 457

X

- 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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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-Publisher FASB
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-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of asset retirement obligations (ARO) costs incurred (whether capitalized or charged to expense) during the period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
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