Price Risk Management Fair values of price risk management assets and liabilities (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Current Assets, Commodity Contracts:
Electricity	$ 6	$ 4
Natural gas	3	9
Total current derivative assets	9	13
Noncurrent Assets, Commodity Contracts: [Abstract]
Electricity	1	1
Natural gas	0	2
Total noncurrent derivative assets	1	3
Total derivative assets not designated as hedging instruments	10	16
Total derivative assets	10	16
Current Liabilities, Commodity Contracts: [Abstract]
Electricity	56	77
Natural gas	107	111
Total current derivative liabilities	163	188
Noncurrent Liabilities, Commodity Contracts: [Abstract]
Electricity	37	42
Natural gas	106	146
Total noncurrent derivative liabilities	143	188
Total derivative liabilities not designated as hedging instruments	306	376
Total derivative liabilities	$ 306	$ 376

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to natural gas which are expected to be settled within a year or normal operating cycle, if longer.

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to electricity which are expected to be settled after a year or beyond the normal operating cycle, if longer.

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to natural gas which are expected to be settled after a year or beyond the normal operating cycle, if longer.

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Carrying amount as of the balance sheet date of the liability arising from commodity contracts related to electricity which are expected to be settled within a year or the normal operating cycle, if longer.

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Carrying amount as of the balance sheet date of the liability arising from the commodity contracts related to natural gas which are expected to be settled within a year or normal operating cycle, if longer.

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Carrying amount as of the balance sheet date of the liability arising from commodity contracts related to electricity which are expected to be settled after a year or beyond the normal operating cycle, if longer.

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Commodity contracts: [Abstract]

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Fair valules as of the balance sheet date for all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be settled within one year or the normal operating cycle, if longer.

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Fair values as of the balance sheet date for all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be settled within one year of the normal operating cycle, if longer.

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Current Liabilities, Commodity Contracts: [Abstract]

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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.

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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.

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Noncurrent Assets, Commodity Contracts: [Abstract]

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Fair values as of the balance sheet date for all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be settled after one year or normal operating cycle, if longer.

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Fair value as of the balance sheet date of all price risk derivative assets not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

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+ References

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