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Stock-Based Compensation (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | three years |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 6,000,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee | 500,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 3,884,919 |  |
Consumers Energy Company [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | three years |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 6,000,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee | 500,000 |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 3,884,919 |  |
Minimum [Member] |  |  |
Percent of Initial Grant Issued on Vesting Date | 0.00% |  |
Minimum [Member] | Consumers Energy Company [Member] |  |  |
Percent of Initial Grant Issued on Vesting Date | 0.00% |  |
Maximum [Member] |  |  |
Percent of Initial Grant Issued on Vesting Date | 200.00% |  |
Maximum [Member] | Consumers Energy Company [Member] |  |  |
Percent of Initial Grant Issued on Vesting Date | 200.00% |  |
TSR Restricted Stock [Member] |  |  |
Share Based Compensation Arrangement By Share Based Payment Award, Percentage | 75.00% | 67.00% | 67.00%
TSR Restricted Stock [Member] | Consumers Energy Company [Member] |  |  |
Share Based Compensation Arrangement By Share Based Payment Award, Percentage | 75.00% | 67.00% | 67.00%
Time-Lapsed Restricted Stock [Member] |  |  |
Share Based Compensation Arrangement By Share Based Payment Award, Percentage | 25.00% | 33.00% | 33.00%
Time-Lapsed Restricted Stock [Member] | Consumers Energy Company [Member] |  |  |
Share Based Compensation Arrangement By Share Based Payment Award, Percentage | 25.00% | 33.00% | 33.00%

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- Definition Percentage of initial grant of equity-based compensation awards earned depending on the outcome of the market condition. + References No definition available. + Details
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- Definition Share Based Compensation Arrangement By Share Based Payment Award, Percentage + References No definition available. + Details
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- Definition Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph a -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 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The highest quantity of shares an employee can purchase under the plan per period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph a -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 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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