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Price Risk Management Counterparties Representing 10% or More (Details)	Jun. 30, 2011	Dec. 31, 2010
Assets from price risk management activities:
Counterparty A	24.00%	22.00%
Counterparty B	13.00%	11.00%
Counterparty C	12.00%	23.00%
Counterparty D	10.00%	1.00%
Counterparty E	0.00%	10.00%
Concentration of Risk, Derivative Instruments, Assets	59.00%	67.00%
Liabilities from price risk management activities:
Counterparty C	25.00%	24.00%
Counterparty F	10.00%	9.00%
Counterparty G	9.00%	12.00%
Concentration of Risk, Derivative Instruments, Liabilities	44.00%	45.00%

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Assets from price risk management activities: [Abstract]

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Represents aggregate of individually significant counterparties of total assets arising from derivative instruments from price risk management activities.

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Represents aggregate of individually significant counterparties of total liabilities arising from derivative instruments from price risk management activities.

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Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

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Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

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Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

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Individually significant counterparty of total liabilities arising from derivative instruments from price risk management activities.

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Individually significant counterparty of total assets arising from dreivative instruments from price risk management activities.

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Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

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Individually significant counterparty of total liabilities arising from derivative instruments from price risk management activities.

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Individually significant counterparty of total liabilities arising from derivative instruments from price risk management activities.

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Liabilities from price risk management activities: [Abstract]

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