Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation, Revision of Estimate	$ 27	$ 0	$ 5
Asset Retirement Obligation, Accretion Expense	8	7	7
Asset Retirement Obligation, Liabilities Incurred	0	$ 2	$ 1
Decommissioning Liability, Noncurrent	4
Asset Retirement Obligation, Cash Paid to Settle	4
Litigation Settlement, Amount Awarded from Other Party	89
Asset Retirement Obligation, Period Increase (Decrease)	3
Asset Retirement Obligation Rate Recovery related to Trojan Plant	4
Property, Plant and Equipment, Other Types [Member]
Asset Retirement Obligation, Revision of Estimate	4
Utility Plant [Domain]
Asset Retirement Obligation, Revision of Estimate	23
Asset Retirement Obligation, Accretion Expense	4
Asset Retirement Obligation, Liabilities Incurred	$ 1

Asset Retirement Obligation Rate Recovery related to Trojan Plant

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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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-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

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- Definition

Amount of cash paid during the period to settle an asset retirement obligation. Amounts paid to settle an asset retirement obligation are generally included in the operating section of the Statement of Cash Flows.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 17
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3367-108585

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Amount of asset retirement obligations incurred during the period.

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 410
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- Definition

Amount of a decommissioning liability associated with a legal obligation that a firm incurs when it constructs or operates an asset that must eventually be withdrawn from active service. This may include operating assets such as nuclear power plants or shipping vessels.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Amount awarded from other party in judgment or settlement of litigation.

+ References

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