Derivative Instruments (Details 1) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative Assets
Fair Value	$ 305	$ 296
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	(171)	(150)
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	(4)	(5)
Net Fair Value	130	141
Derivative Liabilities
Fair Value	(573)	(597)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	171	150
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	13
Net Fair Value	(402)	(434)
Power Contracts
Derivative Assets
Fair Value	262	252
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	(169)	(142)
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	(4)	(5)
Net Fair Value	89	105
Derivative Liabilities
Fair Value	(175)	(151)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	169	142
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	9
Net Fair Value	(6)	0
FTRs
Derivative Assets
Fair Value	2	8
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	(2)	(8)
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	0
Net Fair Value	0	0
Derivative Liabilities
Fair Value	(5)	(9)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	2	8
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0	1
Net Fair Value	(3)	0
NUGs
Derivative Assets
Fair Value	34	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	34	36
Derivative Liabilities
Fair Value	(247)	(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	(247)	(290)
LCAPP
Derivative Liabilities
Fair Value	(146)	(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	(146)	(144)
Other
Derivative Assets
Fair Value	7
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments	0
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged	0
Net Fair Value	7
Derivative Liabilities
Fair Value		(3)
Amounts Not Offset in Consolidated Balance Sheet, Derivative Instruments		0
Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received)/Pledged		3
Net Fair Value		$ 0

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Derivative Assets, Fair Value, Amounts Offset Against Derivative Liabilities

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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 815

-SubTopic 10

-Section 45

-Paragraph 6

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-Publisher FASB

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-Number FIN39-1

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-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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-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.

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

-Publisher FASB

-Name Accounting Standards Codification

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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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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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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

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-Paragraph 8

-Subparagraph (a)

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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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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.

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