Impairment of Long-lived Assets (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	3 Months Ended
Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2013 Inventories	Jul. 08, 2013 Hatfield's Ferry, Units 1-3 [Member] MW	Jul. 08, 2013 Mitchell, Units 2-3 [Member] MW
Schedule of Generating Plant Retirements [Line Items]
Megawatt capacity of plants expected to be closed					1,710	370
Impairments of long-lived assets	$ 473	$ 0	$ 473	$ 13

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration