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Regulatory Matters (Schedule of the Components of Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2012 | Dec. 31, 2011
Regulatory assets, current | $ 35 |  | $ 1 |
Regulatory assets, noncurrent | 2,287 |  | 2,466 |
Regulatory liabilities, current | 25 |  | 125 |
Regulatory liabilities, noncurrent | 2,101 |  | 1,875 |
Consumers Energy Company [Member] |  |  |  |
Regulatory assets, current | 35 |  | 1 |
Regulatory assets, noncurrent | 2,287 |  | 2,466 |
Total regulatory asset | 2,322 |  | 2,467 |
Regulatory liabilities, current | 25 |  | 125 |
Regulatory liabilities, noncurrent | 2,101 |  | 1,875 |
Total regulatory liabilities | 2,126 |  | 2,000 |
Requested Energy Optimization Incentive for Exceeding Savings Targets | 17 |  |  |
DOE Settlement [Member] | Consumers Energy Company [Member] |  |  |  |
Current Regulatory Liability Recovery End Date | 2013 |  |  |
Regulatory liabilities, current | 23 |  | 120 |
Cost Of Removal [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory liabilities, noncurrent | 1,441 |  | 1,364 |
Income Taxes, Net [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory liabilities, noncurrent | 336 |  | 181 |
Renewable Energy Plan [Member] | Consumers Energy Company [Member] |  |  |  |
Noncurrent Regulatory Liability, Recovery End Date | 2028 |  |  |
Regulatory liabilities, noncurrent | 175 |  | 161 |
ARO [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory liabilities, noncurrent | 103 |  | 113 |
Energy Optimization Plan [Member] | Consumers Energy Company [Member] |  |  |  |
Noncurrent Regulatory Liability, Recovery End Date | 2014 |  |  |
Regulatory liabilities, noncurrent | 34 |  | 45 |
Other Regulatory Liabilities [Member] | Consumers Energy Company [Member] |  |  |  |
Current Regulatory Liability Recovery End Date | 2013 |  |  |
Regulatory liabilities, current | 2 |  | 5 |
Regulatory liabilities, noncurrent | 12 |  | 11 |
Postretirement Benefits [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory assets, noncurrent | 1,700 | [1] | 1,665 | [1]
Securitized Costs [Member] | Consumers Energy Company [Member] |  |  |  |
Noncurrent Regulatory Asset Recovery End Date | 2016 | [2] |  |
Regulatory assets, noncurrent | 192 | [2] | 252 | [2]
MGP Sites [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory assets, noncurrent | 152 | [2] | 156 | [2]
ARO [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory assets, noncurrent | 123 | [3] | 114 | [3]
Unamortized Debt Costs [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory assets, noncurrent | 55 | [2] | 44 | [2]
Gas Revenue Decoupling Mechanism 2011-2012 [Member] | Consumers Energy Company [Member] |  |  |  |
Noncurrent Regulatory Asset Recovery End Date | 2014 |  |  |
Regulatory assets, noncurrent | 17 |  | 21 |
Energy Optimization Plan Incentive [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory Current Asset, End Date for Recovery | 2013 |  |  |
Noncurrent Regulatory Asset Recovery End Date | 2014 |  |  |
Regulatory assets, current | 15 |  |  |
Regulatory assets, noncurrent | 17 |  | 26 |
Gas Storage Inventory Adjustments [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory assets, noncurrent | 15 | [2] | 14 | [2]
2010-2011 Gas Revenue Decoupling Mechanism [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory Current Asset, End Date for Recovery | 2013 |  |  |
Regulatory assets, current | 16 |  |  |
Cancelled Coal-Fueled Plant Costs [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory Current Asset, End Date for Recovery | 2013 | [4] |  |
Noncurrent Regulatory Asset Recovery End Date | 2015 | [4] |  |
Regulatory assets, current | 4 | [4] |  |
Regulatory assets, noncurrent | 7 | [4] |  |
Major Maintenance [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory assets, noncurrent | 5 | [4] |  |
Big Rock Decommissioning [Member] | Consumers Energy Company [Member] |  |  |  |
Noncurrent Regulatory Asset Recovery End Date | 2012 | [2] |  |
Regulatory assets, noncurrent |  |  | 85 | [2]
Electric Revenue Decoupling Mechanism [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory assets, noncurrent |  |  | 59 |
Stranded Costs [Member] | Consumers Energy Company [Member] |  |  |  |
Noncurrent Regulatory Asset Recovery End Date | 2012 | [4] |  |
Regulatory assets, noncurrent |  |  | 23 | [4]
Other Regulatory Assets [Member] | Consumers Energy Company [Member] |  |  |  |
Regulatory Current Asset, End Date for Recovery | 2012 | [4] |  |
Regulatory assets, current |  |  | 1 | [4]
Regulatory assets, noncurrent | $ 4 | [4] | $ 7 | [4]
[1] | This regulatory asset is offset partially by liabilities. The net amount is included in rate base, thereby providing a return.
[2] | These regulatory assets represent expenditures for which the MPSC has provided, or Consumers expects, recovery without a return on investment.
[3] | Consumers records a regulatory asset and a regulatory liability for timing differences between the recognition of AROs for financial reporting purposes and the recovery of these costs from customers. Although the regulatory asset for AROs does not provide a return on investment, the underlying asset retirement costs are capitalized as part of the carrying amount of the related asset and included in rate base, thereby providing a return.
[4] | These regulatory assets either are included in rate base (or are expected to be included, for costs incurred subsequent to the most recently approved rate case), thereby providing a return on expenditures, or provide a specific return on investment authorized by the MPSC.

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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9, 10 -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 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9, 10 -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 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 11 -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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