Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2011
Variable interest Entities [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	$ 6		$ 6
Variable Interest Entity, Consolidated, Carrying Amount, Cash and Cash Equivalents	1		1
Variable Interest Entity, Consolidated, Carrying Amount, Electric Utility Plant, Net	5		5
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	1.00%
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest	99.00%
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions	100.00%
Estimated Remaining Useful Life of Facility Acquired	75.00%
Variable Interest Entity, Initial Consolidation, Gain (Loss)		$ 4
Variable Interest Entity, Discount Rate Used in Impairment Calc	7.00%

Estimated useful life expected to be remaining at the date of purchase in a future period.

No definition available.

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- Details

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- Definition

The carrying amount of the consolidated variable interest entities' cash and cash equivalents included in the reporting entity's statement of financial position.

+ References

No definition available.

+ Details

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- Definition

The carrying amount of the variable interest entities' electric utility plant, net included in the reporting entity's consolidated statement of financial position.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Discount rate used in connection with impairment calculation for solar facilities owned by VIEs, which represents the reporting entity's allowed rate of return.

+ References

No definition available.

+ Details

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- Definition

The number of units or percentage investment held by one or more members or limited partners of the LLC or LP.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 272

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

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- Definition

Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions.

+ References

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section H

+ Details

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- Definition

The net carrying amount of the consolidated Variable Interest Entity's assets and liabilities included in the reporting entity's statement of financial position.

+ References

No definition available.

+ Details

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- Definition

The gain (loss) recognized on initial consolidation of a variable interest entity (VIE) when the VIE is not a business (as defined).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5710-111685

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS140-4/FIN46(R)-8

-Paragraph C5

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Balance Type:	credit
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- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 5A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7880789&loc=SL6759159-111685

+ Details

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