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Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended
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Mar. 31, 2012 | Dec. 31, 2011 | Mar. 31, 2012 Consumers Energy Company [Member] | Dec. 31, 2011 Consumers Energy Company [Member] | Oct. 31, 2011 Consumers Energy Company [Member] | Mar. 31, 2012 2011 Electric Rate Case [Member] Consumers Energy Company [Member] | Dec. 31, 2011 2011 Electric Rate Case [Member] Consumers Energy Company [Member] | Nov. 30, 2011 2011 Electric Rate Case [Member] Consumers Energy Company [Member] | Jun. 30, 2011 2011 Electric Rate Case [Member] Consumers Energy Company [Member] | Mar. 31, 2011 2009-2010 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Mar. 31, 2012 2010-2011 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Mar. 31, 2012 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Sep. 30, 2011 2010-2011 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Mar. 31, 2012 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Mar. 31, 2012 Big Rock Decommissioning And Related Costs [Member] Consumers Energy Company [Member] | Sep. 30, 2011 Big Rock Decommissioning And Related Costs [Member] Consumers Energy Company [Member] | Apr. 30, 2010 Big Rock Decommissioning And Related Costs [Member] Consumers Energy Company [Member] | Mar. 31, 2012 DOE Settlement [Member] Consumers Energy Company [Member] | Jul. 31, 2011 Nuclear Fuel Disposal Cost [Member] Consumers Energy Company [Member]
Annual Rate Increase Requested by Consumers |  |  |  |  |  |  |  |  | $ 195 |  |  |  |  |  |  |  |  |  |
Requested Recovery |  |  |  |  |  |  |  |  |  | 27 | 32 |  | 16 |  |  |  |  |  |
Write-Off of Regulatory Asset |  |  |  |  |  |  |  |  |  |  |  | 59 |  |  |  |  |  |  |
Regulatory assets, noncurrent | 2,362 | 2,466 | 2,362 | 2,466 |  |  |  |  |  |  |  |  |  | 28 | 85 |  |  |  |
Amount Paid to Transfer Ownership and Responsibility |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 |  |  |  |
Regulatory liabilities | 120 | 125 | 120 | 125 |  |  |  |  |  |  |  |  |  |  |  |  |  | 120 |
Proposed Amended Annual Renewable Energy Plan Surcharge Billed To Customers |  |  |  |  | 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation Settlement, Gross |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 120
Proposed Recovery Of Regulatory Asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 85 |  |  |
Proposed Refund Of Spent Nuclear Fuel Disposal Costs Collected |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 23 |  |  |
Remaining Portion of Litigation Settlement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 |  |  |
Revenue Collected in Excess of the Costs Incurred to Decommission Big Rock, Plus Interest, and Ordered for Refund |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 85 |  |
Nuclear Fuel Storage Costs Incurred as a Result of the DOE's Failure to Accept Spent Nuclear Fuel |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 55 |  |  |  |
Proposed Annual Amount Of Reduction Of Renewable Energy Plan Surcharge Billed To Customers |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Energy Optimization Incentive to be Requested for Exceeding 2011 Savings Targets |  |  | 15 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of Return on Equity Requested by Consumers |  |  |  |  |  |  |  |  | 10.70% |  |  |  |  |  |  |  |  |  |
Annual Rate Increase Recommended |  |  |  |  |  | 43 |  |  |  |  |  |  |  |  |  |  |  |  |
Rate Of Return On Equity Recommended |  |  |  |  |  | 10.25% |  |  |  |  |  |  |  |  |  |  |  |  |
Annual Rate Increase Self-Implemented by Consumers |  |  |  |  |  |  | 118 |  |  |  |  |  |  |  |  |  |  |  |
Amount Of Proposed Self-implemented Rate Increase |  |  |  |  |  |  |  | 147 |  |  |  |  |  |  |  |  |  |  |
Amount Of Self-Implemented Rate Increase Authorized By the MPSC |  |  |  |  |  |  | $ 118 |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition The annual rate increase proposed to self-implement. + References No definition available. + Details
Name: | cms_AmountOfProposedSelfImplementedRateIncrease
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The annual rate increase authorized to self-implement. + References No definition available. + Details
Name: | cms_AmountOfSelfImplementedRateIncreaseAuthorizedByMpsc
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The amount that Consumers paid to transfer ownership and responsibility for the Big Rock ISFSI + References No definition available. + Details
Name: | cms_AmountPaidToTransferOwnershipAndResponsibility
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The annual rate increase recommended by the Administrative Law Judge. + References No definition available. + Details
Name: | cms_AnnualRateIncreaseRecommended
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The annual rate increase requested by Consumers. + References No definition available. + Details
Name: | cms_AnnualRateIncreaseRequested
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The annual rate increase self-implemented by Consumers. + References No definition available. + Details
Name: | cms_AnnualRateIncreaseSelfImplemented
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Energy optimization incentive to be requested for achieving electric and gas savings targets. + References No definition available. + Details
Name: | cms_EnergyOptimizationIncentiveToBeRequested
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Nuclear fuel storage costs incurred by Consumers as a result of the DOE's failure to accept spent nuclear fuel. + References No definition available. + Details
Name: | cms_NuclearFuelStorageCostsIncurred
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The proposed amended annual renewable energy plan surcharge billed to customers. + References No definition available. + Details
Name: | cms_ProposedAmendedAnnualRenewableEnergyPlanSurchargeBilledToCustomers
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The annual amount by which the renewable energy plan surcharge billed to customers will be reduced. + References No definition available. + Details
Name: | cms_ProposedAnnualAmountOfReductionOfRenewableEnergyPlanSurchargeBilledToCustomers
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The portion of the settlement proceeds Consumers has requested to use as recovery for its Big Rock Nuclear Decommissioning And Related Costs regulatory asset. + References No definition available. + Details
Name: | cms_ProposedRecoveryOfRegulatoryAsset
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of spent nuclear fuel disposal costs incurred and collected from customers through rates that Consumers has proposed to refund. + References No definition available. + Details
Name: | cms_ProposedRefundOfSpentNuclearFuelDisposalCostsCollected
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The rate of return on equity recommended by the Administrative Law Judge. + References No definition available. + Details
Name: | cms_RateOfReturnOnEquityRecommended
Namespace Prefix: | cms_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The rate of return on equity requested by Consumers. + References No definition available. + Details
Name: | cms_RateOfReturnOnEquityRequested
Namespace Prefix: | cms_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The remaining portion of the settlement proceeds received from the DOE. + References No definition available. + Details
Name: | cms_RemainingPortionOfLitigationSettlement
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount for which Consumers requested recovery. + References No definition available. + Details
Name: | cms_RequestedRecovery
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Revenue collected in excess of the costs incurred to decommission, plus interest, and for which the MPSC ordered a refund. + References No definition available. + Details
Name: | cms_RevenueCollectedInExcessOfCostsToDecommissionPlusInterest
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Write-Off of the value of Consumers' electric revenue decoupling mechanism regulatory asset. + References No definition available. + Details
Name: | cms_WriteOffOfRegulatoryAsset
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This element represents the gross amount awarded, to be received by, or to be remitted to the entity in settlement of litigation occurring during the period. + References No definition available. + Details
Name: | us-gaap_LitigationSettlementGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. + 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
Name: | us-gaap_RegulatoryAssetsNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current 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
Name: | us-gaap_RegulatoryLiabilityCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant