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Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified |  |  |  |  |  |  | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009 | Dec. 31, 2011 Consumers Energy Company [Member] | Dec. 31, 2010 Consumers Energy Company [Member] | Dec. 31, 2009 Consumers Energy Company [Member] | Dec. 31, 2010 2009 Interest Dispute [Member] | Dec. 31, 2010 2009 Interest Dispute [Member] Consumers Energy Company [Member] | Dec. 31, 2010 2009 Audit [Member] | Dec. 31, 2010 Changes to Taxable Income [Member] 2009 Audit [Member] | Dec. 31, 2010 Decrease Operating Loss Carryforward [Member] 2009 Audit [Member] | Dec. 31, 2010 Increase Taxable Income [Member] 2009 Audit [Member] | Dec. 31, 2011 Increase Taxable Income [Member] 2010 Audit [Member]
Uncertain tax benefits | $ 4 | $ 4 | $ 8 | $ 4 | $ 3 | $ 3 |  |  |  |  |  |  |
Accrued interest, less than | 0 | 1 | 1 | 0 | 1 | 1 |  |  |  |  |  |  |
Results of IRS audit |  |  |  |  |  |  | 6 | 4 | 15 | 132 | 82 | 50 |
Remaining interest balance |  |  |  |  |  |  | 3 | 1 |  |  |  |  |
Expected number of months until settlement on tax credit claim |  |  |  |  |  |  |  |  |  |  |  |  | 12
Research and development tax credit claim |  |  |  |  |  |  |  |  |  |  |  |  | $ 21

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- Definition The tax effect as of the balance sheet date of the amount of future tax deductions arising from unused research tax credit carryforwards; a tax credit carryforward is the amount by which tax credits available for utilization exceed statutory limitations for inclusion in historical filings, and which can only be utilized if sufficient tax-basis income is generated in future periods and providing tax laws continue to allow such utilization. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition Reflects the effects of adjustments of previously recorded tax expense, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, IRS tax settlement and unusual repatriation of foreign earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 48 -Paragraph 10 -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. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 48 -Paragraph 10A, 10B, 10C -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 -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition This element represents the amount of interest expense accrued as of the date of the statement of financial position for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 48 -Paragraph 21 -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 FASB Interpretation (FIN) -Number 48 -Paragraph 15 -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 -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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