Jointly Owned Plants (Details) $ in Millions	Dec. 31, 2016 USD ($)
South Texas Project
Jointly Owned Utility Plant Interests
Ownership Interest (as a percent)	44.00%
Property, Plant and Equipment	$ 3,275
Accumulated Depreciation	(1,734)
Construction in Progress	$ 39
Big Cajun II Unit 3, New Roads, LA
Jointly Owned Utility Plant Interests
Ownership Interest (as a percent)	58.00%
Property, Plant and Equipment	$ 204
Accumulated Depreciation	123
Construction in Progress	$ 0
Cedar Bayou Unit 4, Baytown, TX
Jointly Owned Utility Plant Interests
Ownership Interest (as a percent)	50.00%
Property, Plant and Equipment	$ 216
Accumulated Depreciation	(67)
Construction in Progress	$ 5
Keystone [Member]
Jointly Owned Utility Plant Interests
Ownership Interest (as a percent)	3.70%
Property, Plant and Equipment	$ 97
Accumulated Depreciation	(48)
Construction in Progress	$ 0
Conemaugh, New Florence, PA
Jointly Owned Utility Plant Interests
Ownership Interest (as a percent)	3.72%
Property, Plant and Equipment	$ 103
Accumulated Depreciation	(51)
Construction in Progress	$ 1

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

+ References

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- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

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- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

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