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Derivative Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified |  |  |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | --- | ---
Sep. 30, 2011 | Dec. 31, 2010 | Sep. 30, 2011 Forward Contracts [Member] | Sep. 30, 2011 Forward Contracts to Purchase [Member] | Sep. 30, 2011 Forward Contracts to Sell [Member] | Sep. 30, 2011 Option Contract to Sell [Member] | Sep. 30, 2011 Consumers Energy Company [Member] Financial Transmission Right [Member] | Sep. 30, 2010 Consumers Energy Company [Member] Financial Transmission Right [Member] | Sep. 30, 2011 Consumers Energy Company [Member] Financial Transmission Right [Member] | Sep. 30, 2010 Consumers Energy Company [Member] Financial Transmission Right [Member]
Derivative contracts (GWh/bcf) |  |  | 574.0 | 4.4 | 7.5 | 151.0 |  |  |  |
Gain Or Loss Deferred In Regulatory Accounts |  |  |  |  |  |  | $ 1 | $ 3 | $ 2 | $ 4
Derivative Liabilities Subject to Credit-Related-Contingent Features (less than at 9/30/2011) | 1 | 1 |  |  |  |  |  |  |  |
Loss Exposure to Counterparties for Derivative Instruments less than | $ 1 |  |  |  |  |  |  |  |  |

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- Definition The amount of gain or loss for the period deferred and recognized as a regulatory asset (for a loss) or liability (for a gain). + Details
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Period Type: | duration

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- Definition The amount of loss for contracts accounted for as derivative assets that would be incurred if counterparties failed to meet their contractual obligations. + Details
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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 + Details
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- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44D -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. + Details
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