Fair Value of Financial Assets and Liabilities (Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Unobservable Inputs) (Details) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Beginning balance	$ 146	$ 248	$ 146	$ 223
Revenue, non-regulated electric, natural gas, and other	(11)	(73)	(19)	(29)
Fuel used in electric generation and purchased power-non-regulated, fair value		(8)		(11)
Gains (losses) on available for sale securities and other	(1)	5	5	10
Losses on commodity cash flow hedges		(1)
Purchases	6		7
Sales	(1)		(3)
Settlements	(28)		(27)
Net purchases, sales, issuances and settlements		35		11
Total gains included on Consolidated Balance Sheet as regulatory asset or liability	19	13	21	15
Transfers out of Level 3	(9)		(9)
Ending Balance	121	219	121	219
Pre-tax revenue, non-regulated electric, natural gas, and other			(10)	16
Pre-tax fuel used in electric generation and purchased power-non-regulated				(1)
Total			(10)	15
Available-for-Sale Auction Rate Securities [Member]
Beginning balance	122	202	118	198
Gains (losses) on available for sale securities and other	(1)	5	5	10
Settlements	(22)		(24)
Net purchases, sales, issuances and settlements		(29)		(30)
Transfers out of Level 3	(9)		(9)
Ending Balance	90	178	90	178
Available-for-Sale NDTF Investments [Member]
Beginning balance	48	25	47
Purchases	6		7
Sales	(1)		(3)
Net purchases, sales, issuances and settlements		23		48
Total gains included on Consolidated Balance Sheet as regulatory asset or liability			2
Ending Balance	53	48	53	48
Derivatives, Net [Member]
Beginning balance	(24)	21	(19)	25
Revenue, non-regulated electric, natural gas, and other	(11)	(73)	(19)	(29)
Fuel used in electric generation and purchased power-non-regulated, fair value		(8)		(11)
Losses on commodity cash flow hedges		(1)
Settlements	(6)		(3)
Net purchases, sales, issuances and settlements		41		(7)
Total gains included on Consolidated Balance Sheet as regulatory asset or liability	19	13	19	15
Ending Balance	(22)	(7)	(22)	(7)
Pre-tax revenue, non-regulated electric, natural gas, and other			(10)	16
Pre-tax fuel used in electric generation and purchased power-non-regulated				(1)
Total			$ (10)	$ 15

Available For Sale Securities And Other Gross Gains Losses Net

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Fuel used in electric generation and purchased power-non-regulated, fair value

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- Definition

The amount of total gains or losses for the period included in earnings that are attributable to the change in unrealized gains or losses relating to those assets and liabilities still held at the reporting date

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- Definition

Total Gains Losses Included On Balance Sheet As Regulatory Asset Or Liability Or As Non Current Liability

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- Definition

Total pre-tax amounts included in the statement of operations related to Level 3

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1)
-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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

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- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

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- Definition

This element represents purchases, sales, issuances, and settlements (net) which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

+ Details

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- Definition

Sales that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

+ Details

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- Definition

Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

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- Definition

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c
-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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open agreements to purchase or sell mineral resources, energy, and agricultural products at some future point held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 28
-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 2: 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=6943989&loc=d3e3602-108585

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