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Regulatory Matters (Narrative) (Details) (USD $) |  |  |  |  |  | 1 Months Ended |  |  |  |  |  |  |  |  |  | 1 Months Ended |  |  |  |  |  |  |  |  |  |
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Sep. 30, 2011 | Dec. 31, 2010 | Jun. 30, 2011 Consumers Energy Company [Member] 2010 Electric Rate Case [Member] | Dec. 31, 2010 Consumers Energy Company [Member] 2010 Electric Rate Case [Member] | Jun. 30, 2011 2011 Electric Rate Case [Member] Consumers Energy Company [Member] | Jun. 30, 2011 Power Supply Cost Recover (PSCR) [Member] Consumers Energy Company [Member] | Sep. 30, 2011 Consumers Energy Company [Member] Electric Decoupling [Member] | Mar. 31, 2011 Consumers Energy Company [Member] Electric Decoupling [Member] | Mar. 31, 2011 Consumers Energy Company [Member] Uncollectible Expense Tracking Mechanism [Member] | Jun. 30, 2011 Consumers Energy Company [Member] Electric Operation and Maintenance Show-Cause Order [Member] | Dec. 31, 2009 Consumers Energy Company [Member] Electric Operation and Maintenance Show-Cause Order [Member] | May 31, 2011 2010 Gas Rate Case [Member] Consumers Energy Company [Member] | Feb. 28, 2011 2010 Gas Rate Case [Member] Consumers Energy Company [Member] | Jan. 31, 2011 2010 Gas Rate Case [Member] Consumers Energy Company [Member] | Aug. 31, 2010 2010 Gas Rate Case [Member] Consumers Energy Company [Member] | Sep. 30, 2011 2011 Gas Rate Case [Member] Consumers Energy Company [Member] | Sep. 30, 2011 Consumers Energy Company [Member] Gas Decoupling [Member] | Sep. 30, 2011 Consumers Energy Company [Member] Big Rock Decommissioning [Member] | Jul. 31, 2011 Consumers Energy Company [Member] Big Rock Decommissioning [Member] | Apr. 30, 2010 Consumers Energy Company [Member] Big Rock Decommissioning [Member] | Feb. 28, 2010 Consumers Energy Company [Member] Big Rock Decommissioning [Member] | Jun. 30, 2011 Consumers Energy Company [Member] Electric Plant [Member] | Feb. 28, 2010 Consumers Energy Company [Member] Consumers Share of Ludington [Member] | Oct. 31, 2011 Consumers Energy Company [Member] | Sep. 30, 2011 Consumers Energy Company [Member] | Jun. 30, 2011 Consumers Energy Company [Member] | May 31, 2011 Consumers Energy Company [Member] | Apr. 30, 2011 Consumers Energy Company [Member] | Dec. 31, 2010 Consumers Energy Company [Member]
Annual Rate Increase Authorized by the MPSC |  |  |  | $ 146,000,000 |  |  |  |  |  |  |  | $ 31,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual Rate Increase Requested by Consumers |  |  |  |  | 195,000,000 |  |  |  |  |  |  |  |  |  | 55,000,000 | 49,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Difference Between the Annual Rate Increase Authorized by MPSC and the Annual Rate Increase Self-implemented by Consumers |  |  |  | 4,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of rates to be refunded to customers |  |  | 0 |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested Recovery |  |  |  |  |  |  |  | 27,000,000 | 3,000,000 |  |  |  |  |  |  |  | 16,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets | 2,002,000,000 | 2,093,000,000 |  |  |  |  | 55,000,000 |  |  |  |  |  |  |  |  |  | 16,000,000 | 85,000,000 |  |  |  |  |  |  | 2,002,000,000 |  |  |  | 2,093,000,000
Litigation Settlement, Gross |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 120,000,000 |  |  |  |  |  |  |  |  |  |
Proposed Refund Of Spent Nuclear Fuel Disposal Costs Collected |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 23,000,000 |  |  |  |  |  |  |  |  |  |  |
Remaining Portion of Litigation Settlement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12,000,000 |  |  |  |  |  |  |  |  |  |  |
Percentage of Difference Between Rate Base Expense and Actual Expense To Collect/Refund |  |  |  |  |  |  |  |  | 80.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Difference Between the Operation and Maintenance Expenditures Ordered by the MPSC and the Operation and Maintenance Expenditures Incurred by Consumers During 2007 |  |  |  |  |  |  |  |  |  |  | 14,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Imposed fine by MPSC |  |  |  |  |  |  |  |  |  | 65,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contributions to Fund Decommissioning Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 44,000,000 |  |  |  |  |  |  |  |
Revenue Collected in Excess of Costs to Decommission Big Rock, Plus Interest, and Ordered for Refund |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 85,000,000 |  |  |  |  |  |  |  |  |
Amount Paid to Transfer Ownership and Responsibility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,000,000 |  |  |  |  |  |  |  |  |  |  |
Nuclear Fuel Storage Costs Incurred as a Result of the DOE's Failure to Accept Spent Nuclear Fuel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 55,000,000 |  |  |  |  |  |  |  |  |  |  |
Recommended Disallowance of Renewable Energy Plan Expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,000,000 |  |  |
Annual Amount Of Reduction Of Renewable Energy Plan Surcharge Billed To Customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 54,000,000 |  |
Proposed Annual Amount Of Reduction Of Renewable Energy Plan Surcharge Billed To Customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,000,000 |  |  |  |  |
Authorized Energy Optimization Incentive for Exceeding 2009 Savings Targets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,000,000 |  |
Requested Energy Optimization Incentive for Exceeding 2010 Savings Targets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 |
Increase in Annual Depreciation Requested by Consumers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,000,000 |  |  |  |  |  |
Increase in Annual Depreciation Expense Authorized by the MPSC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 19,000,000 |  |  |  |  |  |  |
Rate of Return on Equity Requested by Consumers |  |  |  |  | 10.70% |  |  |  |  |  |  |  |  |  | 11.00% | 10.70% |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of Return On Equity Authorized by the MPSC |  |  |  |  |  |  |  |  |  |  |  | 10.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Over/(Under) Recovery, Including Interest, Authorized by the MPSC |  |  |  |  |  | (31,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount Of Proposed Self-implemented Rate Increase |  |  |  |  |  |  |  |  |  |  |  |  |  | 48,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revised Amount Of Proposed Self-implemented Rate Increase |  |  |  |  |  |  |  |  |  |  |  |  | $ 29,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition The annual rate increase proposed to self-implement. + Details
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- Definition The amount that Consumers paid to transfer ownership and responsibility for the Big Rock ISFSI + Details
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- Definition The annual amount by which the renewable energy plan surcharge billed to customers will be reduced + Details
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Namespace Prefix: | cms
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- Definition The annual rate increase authorized by the MPSC. + Details
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Period Type: | instant

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- Definition The annual rate increase requested by Consumers. + Details
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- Definition Energy optimization incentive that the MPSC authorized Consumers to collect for achieving electric and gas savings targets. + Details
Name: | cms_AuthorizedEnergyOptimizationIncentive
Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The contribution to fund decommissioning costs. + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The difference between the annual rate increase authorized and self-implemented annual rate increase. + Details
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Period Type: | instant

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- Definition The difference between the operation and maintenance expenditures authorized by the MPSC and the operation and maintenance expenditures incurred by Consumers. + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Imposed fine. + Details
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Balance Type: | debit
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- Definition Increase in annual depreciation expense authorized by the MPSC. + Details
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- Definition Increase in annual depreciation expense requested by Consumers. + Details
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- Definition Net over-/(under-) recovery of expense, including interest, authorized by the MPSC. + Details
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Namespace Prefix: | cms
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- Definition Nuclear fuel storage costs incurred by Consumers as a result of the DOE's failure to accept spent nuclear fuel. + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The percentage of the difference between the level of expense included in rates and actual expense that will be collected or refunded. + Details
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Namespace Prefix: | cms
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition The annual amount by which the renewable energy plan surcharge billed to customers will be reduced. + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Proposed Refund Of Spent Nuclear Fuel Disposal Costs Collected + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The rate of return on equity authorized by the Public Service Commission. + Details
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Namespace Prefix: | cms
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition The rate of return on equity requested by Consumers. + Details
Name: | cms_RateOfReturnOnEquityRequested
Namespace Prefix: | cms
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Period Type: | instant

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- Definition Recommended Disallowance Of Renewable Energy Plan Expenditures + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The remaining portion of the settlement proceeds received from the DOE. + Details
Name: | cms_RemainingPortionOfLitigationSettlement
Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Energy optimization incentive requested for achieving electric and gas savings targets. + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The amount for which Consumers requested recovery. + Details
Name: | cms_RequestedRecovery
Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Revenue collected in excess of the costs incurred to decommission, plus interest, and for which the MPSC ordered a refund. + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The revised annual rate increase proposed to self-implement. + Details
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Namespace Prefix: | cms
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Current regulatory liabilities generally represent obligations to make refunds to customers for various reasons including overpayment. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- 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. + Details
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Namespace Prefix: | us-gaap
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- 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
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