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 [Line Items]
Property, Plant and Equipment, Gross	$ 5,364us-gaap_PropertyPlantAndEquipmentGross	$ 4,815us-gaap_PropertyPlantAndEquipmentGross
Accumulated depreciation and amortization	1,554	1,379
Property, Plant and Equipment, Net	3,810us-gaap_PropertyPlantAndEquipmentNet	3,436us-gaap_PropertyPlantAndEquipmentNet
Depreciation expense	195us-gaap_Depreciation	218us-gaap_Depreciation	267us-gaap_Depreciation
Amortization expense	11us-gaap_AdjustmentForAmortization	12us-gaap_AdjustmentForAmortization	18us-gaap_AdjustmentForAmortization
Total depreciation and amortization expense	206	230	285
Beginning balance	101us-gaap_AssetRetirementObligation	135us-gaap_AssetRetirementObligation
Accretion expense	4	4
Revisions in estimates of cash flows	34	(38)
Ending balance	139us-gaap_AssetRetirementObligation	101us-gaap_AssetRetirementObligation	135us-gaap_AssetRetirementObligation
Natural Gas Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	5,235	4,694
Accumulated depreciation and amortization	1,493	1,324
Natural Gas Distribution [Member] \| Weighted Average [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	33 years
Energy Services [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	84	82
Accumulated depreciation and amortization	31	28
Energy Services [Member] \| Weighted Average [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	27 years
Other property [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	45	39
Accumulated depreciation and amortization	$ 30	$ 27
Other property [Member] \| Weighted Average [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 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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- Definition

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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- 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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Asset Retirement Obligation

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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://www.xbrl.org/2003/role/presentationRef

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-SubTopic 20

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- Definition

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.

+ References

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- Definition

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.

+ References

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- Definition

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.

+ References

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- Definition

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.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 1

-Subparagraph (SX 210.5-02.13)

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- Definition

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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

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- Definition

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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