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Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011
Asset Retirement Obligations Assumed Market Risk Premium | 5.00% |  |  |
Hypothetical Asset Retirement Obligations Liability Increase | $ 16 |  | $ 13 |
Asset Retirement Obligation, Beginning Balance | 254 |  | 245 |
Asset Retirement Obligation, Liabilities Incurred | 7 |  | (2) |
Asset Retirement Obligation, Liabilities Settled | (8) | [1] | (7) | [1]
Asset Retirement Obligation, Accretion Expense | 19 |  | 18 |
Asset Retirement Obligation, Revision of Estimate | 40 |  |  |
Asset Retirement Obligation, Ending Balance | 312 |  | 254 |
Consumers Energy Company [Member] |  |  |  |
Asset Retirement Obligations Assumed Market Risk Premium | 5.00% |  |  |
Hypothetical Asset Retirement Obligations Liability Increase | 16 |  | 13 |
Asset Retirement Obligation, Beginning Balance | 253 |  | 244 |
Asset Retirement Obligation, Liabilities Incurred | 7 |  | (2) |
Asset Retirement Obligation, Liabilities Settled | (8) | [1] | (7) | [1]
Asset Retirement Obligation, Accretion Expense | 19 |  | 18 |
Asset Retirement Obligation, Revision of Estimate | 40 |  |  |
Asset Retirement Obligation, Ending Balance | 311 |  | 253 |
Close Gas Treating Plant and Gas Wells [Member] |  |  |  |
Asset Retirement Obligation, Beginning Balance | 1 |  | 1 |
Asset Retirement Obligation, Liabilities Incurred |  |  |  |
Asset Retirement Obligation, Liabilities Settled |  | [1] |  |
Asset Retirement Obligation, Accretion Expense |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |
Asset Retirement Obligation, Ending Balance | 1 |  | 1 |
Coal Ash Disposal Areas [Member] | Consumers Energy Company [Member] |  |  |  |
Asset Retirement Obligation, Beginning Balance | 70 |  | 66 |
Asset Retirement Obligation, Liabilities Settled | (3) | [1] | (2) | [1]
Asset Retirement Obligation, Accretion Expense | 7 |  | 6 |
Asset Retirement Obligation, Revision of Estimate | 40 |  |  |
Asset Retirement Obligation, Ending Balance | 114 |  | 70 |
Wells at Gas Storage Fields [Member] | Consumers Energy Company [Member] |  |  |  |
Asset Retirement Obligation, Beginning Balance | 1 |  | 1 |
Asset Retirement Obligation, Liabilities Settled | (1) | [1] |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |
Asset Retirement Obligation, Ending Balance |  |  | 1 |
Indoor Gas Services Relocations [Member] | Consumers Energy Company [Member] |  |  |  |
Asset Retirement Obligation, Beginning Balance |  |  | 1 |
Asset Retirement Obligation, Liabilities Settled |  |  | (1) | [1]
Asset Retirement Obligation, Revision of Estimate |  |  |  |
Asbestos Abatement [Member] | Consumers Energy Company [Member] |  |  |  |
Asset Retirement Obligation, Beginning Balance | 42 |  | 40 |
Asset Retirement Obligation, Liabilities Settled | (1) | [1] | (1) | [1]
Asset Retirement Obligation, Accretion Expense | 2 |  | 3 |
Asset Retirement Obligation, Revision of Estimate |  |  |  |
Asset Retirement Obligation, Ending Balance | 43 |  | 42 |
Gas Distribution Cut, Purge, Cap [Member] | Consumers Energy Company [Member] |  |  |  |
Asset Retirement Obligation, Beginning Balance | 140 |  | 136 |
Asset Retirement Obligation, Liabilities Incurred | 4 |  | (2) |
Asset Retirement Obligation, Liabilities Settled | (3) | [1] | (3) | [1]
Asset Retirement Obligation, Accretion Expense | 10 |  | 9 |
Asset Retirement Obligation, Revision of Estimate |  |  |  |
Asset Retirement Obligation, Ending Balance | 151 |  | 140 |
Wind Farm [Member] | Consumers Energy Company [Member] |  |  |  |
Asset Retirement Obligation, Liabilities Incurred | 3 |  |  |
Asset Retirement Obligation, Ending Balance | $ 3 |  |  |
[1] | Cash payments of $8 million in 2012 and $7 million in 2011 were included in other current and non-current assets and liabilities as a component of net cash provided by operating activities in CMS Energy’s and Consumers’ consolidated statements of cash flow.

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- Definition Market risk premium assumed to estimate increase in liability of an asset retirement obligation. No market risk premium was included in ARO fair value estimates because reasonable estimates of market risk premiums could not be made. + References No definition available. + Details
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- Definition Hypothetical increase in liability of an asset retirement obligation for which a risk premium could not be reasonably estimated. + References No definition available. + Details
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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 3, 10, 22 -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 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
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- Definition Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 13, 14 -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 410 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph c(3) -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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- Definition Amount of asset retirement obligations incurred during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph c(1) -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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- Definition Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph c(2) -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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- Definition Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph c(4) -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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