Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets, Current	$ 81us-gaap_RegulatoryAssetsCurrent	$ 39us-gaap_RegulatoryAssetsCurrent
Regulatory Assets, Noncurrent	337us-gaap_RegulatoryAssetsNoncurrent	353us-gaap_RegulatoryAssetsNoncurrent
Total regulatory assets	418us-gaap_RegulatoryAssets	392us-gaap_RegulatoryAssets
Regulatory Liability, Current	11us-gaap_RegulatoryLiabilityCurrent	19us-gaap_RegulatoryLiabilityCurrent
Regulatory Liability, Noncurrent	375us-gaap_RegulatoryLiabilityNoncurrent	329us-gaap_RegulatoryLiabilityNoncurrent
Total regulatory liabilities	386us-gaap_RegulatoryLiabilities	348us-gaap_RegulatoryLiabilities
Interest Capitalized [Abstract]
Minimum period of construction for capitalization of interest	3 months
Minimum total project cost for capitalization of interest	$ 1
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Threshold For Amortization Of Unrecognized Actuarial Gains Losses	10.00%
Pension Benefits [Member]
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Approximate Amortization Period Of Net Actuarial Gain Loss	12 years
Amortization Period Of Difference Between Expected And Actual Return On Plan Assets	5 years
Other Postretirement Benefits [Member]
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Approximate Amortization Period Of Net Actuarial Gain Loss	7 years
Amortization Period Of Unrecognized Prior Service Costs Credits	4 years
Maximum [Member] \| Pension Benefits [Member]
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Threshold For Market Related Value	110.00%
Minimum [Member] \| Pension Benefits [Member]
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Threshold For Market Related Value	90.00%

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 405

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.24)

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Amortization Period Of Difference Between Expected And Actual Return On Plan Assets for calculation of market-related value of plan assets

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Amortization Period Of Unrecognized Prior Service Costs Credits

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Amortization period of net actuarial gain (loss) which is approximately the participants' average remaining future years of service.

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Minimum period of construction for capitalization of interest.

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Minimum total project cost for capitalization of interest.

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Threshold For Amortization Of Unrecognized Actuarial Gains Losses, stated as a percentage of the greater of the benefit obligation or the market-related value of plan assets.

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Threshold For Market Related Value stated as a percentage of the fair value of plan assets as measured at the beginning of the year

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