Derivative Instruments (Details 1) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative Assets
Fair Value	$ 284	$ 296
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	(156)	(150)
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	(5)	(5)
Net Fair Value	123	141
Derivative Liabilities
Fair Value	(591)	(598)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	156	150
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	18	13
Net Fair Value	(417)	(435)
Power Contracts
Derivative Assets
Fair Value	253	252
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	(149)	(142)
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	(5)	(5)
Net Fair Value	99	105
Derivative Liabilities
Fair Value	(168)	(155)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	149	142
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	16	12
Net Fair Value	(3)	(1)
FTRs
Derivative Assets
Fair Value	7	8
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	(7)	(8)
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	0
Net Fair Value	0	0
Derivative Liabilities
Fair Value	(9)	(9)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	7	8
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	2	1
Net Fair Value	0	0
NUGs
Derivative Assets
Fair Value	24	36
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	0	0
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	0
Net Fair Value	24	36
Derivative Liabilities
Fair Value	(256)	(290)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	0	0
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	0
Net Fair Value	(256)	(290)
LCAPP
Derivative Liabilities
Fair Value	(158)	(144)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	0	0
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	0
Net Fair Value	$ (158)	$ (144)

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Derivative Assets, Fair Value, Amounts Offset Against Derivative Liabilities

+ References

No definition available.

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- Definition

Derivative Liabilities, Fair Value, Amounts Offset Against Derivative Assets

+ References

No definition available.

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- Definition

Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

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-Section 45

-Paragraph 5

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FIN39-1

-Paragraph 10A, 10B

-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.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 4, 17

-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.

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- Definition

The amount of the obligation to return cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

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- Definition

The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

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- Definition

The amount as of the balance sheet date of the fair value of derivative assets that in accordance with the entity's accounting policy was offset against an obligation to return cash collateral under a master netting arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (a)

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-Publisher FASB

-Name FASB Staff Position (FSP)

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-Paragraph 10B

-Subparagraph b

-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.

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- Definition

The amount as of the balance sheet date of the fair value of derivative liabilities that in accordance with the entity's accounting policy were offset against the right to reclaim cash collateral under a master netting arrangement.

+ References

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- Definition

Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

+ References

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