Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment, Net, by Type [Abstract]
Total	$ 9,393us-gaap_PropertyPlantAndEquipmentGross	$ 8,741us-gaap_PropertyPlantAndEquipmentGross
Accumulated depreciation	3,050	2,907
Property, plant and equipment, net	6,343us-gaap_PropertyPlantAndEquipmentNet	5,834us-gaap_PropertyPlantAndEquipmentNet
Depreciation, Depletion and Amortization [Abstract]
Depreciation expense	295us-gaap_Depreciation	280us-gaap_Depreciation	265us-gaap_Depreciation
Amortization of securitized regulatory assets	441us-gaap_AmortizationOfRegulatoryAsset	383us-gaap_AmortizationOfRegulatoryAsset	442us-gaap_AmortizationOfRegulatoryAsset
Other amortization	32	22	22
Total depreciation and amortization	768	685	729
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	33us-gaap_AssetRetirementObligation	29us-gaap_AssetRetirementObligation
Accretion expense	1	1
Revisions in estimates of cash flows	2	3
Ending balance	36us-gaap_AssetRetirementObligation	33us-gaap_AssetRetirementObligation	29us-gaap_AssetRetirementObligation
Transmission [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	2,057	1,926
Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	6,170	5,848
Other [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	$ 1,166	$ 967
Weighted Average [Member] \| Transmission [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	41 years
Weighted Average [Member] \| Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	30 years
Weighted Average [Member] \| Other [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	15 years

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.14)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 14

-Article 5

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The expense charged against earnings during the period to allocate the capitalized costs of regulatory assets over the periods expected to benefit from such costs.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Glossary Asset Retirement Obligation

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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.

+ References

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

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Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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The other noncash expense, not otherwise specified in the taxonomy, charged against earnings in the period to allocate the cost of tangible and intangible assets over their remaining economic lives.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

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