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Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended |  | 9 Months Ended |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 12 Months Ended | 1 Months Ended |
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Sep. 30, 2013 | Dec. 31, 2012 | Sep. 30, 2013 Consumers Energy Company [Member] | Dec. 31, 2012 Consumers Energy Company [Member] | May 31, 2013 Electric Rate Case [Member] Consumers Energy Company [Member] | Mar. 31, 2013 Electric Rate Case [Member] Consumers Energy Company [Member] | Jan. 31, 2013 Electric Rate Case [Member] Consumers Energy Company [Member] | Sep. 30, 2012 Electric Rate Case [Member] Consumers Energy Company [Member] | Jun. 30, 2012 Electric Rate Case [Member] Consumers Energy Company [Member] | Dec. 31, 2012 2010-2011 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Aug. 31, 2012 2011-2012 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Sep. 30, 2013 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member] | Dec. 31, 2011 Big Rock Decommissioning [Member] Consumers Energy Company [Member] | Jul. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member] | Dec. 31, 2012 DOE Settlement [Member] Consumers Energy Company [Member] | Jan. 31, 2013 Renewable Energy Grant [Member] Consumers Energy Company [Member] | Sep. 30, 2013 Renewable Energy Grant [Member] Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  | $ 145 | $ 148 |  |  |  |  |  |  |  |  |
Annual rate increase self-implemented |  |  |  |  |  | 110 |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  | 89 |  |  |  | 118 |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  |  | 10.30% |  |  |  | 10.30% |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  |  | 10.50% |  |  |  |  |  |  |  |  |
Regulatory assets, noncurrent | 1,579 | 2,287 | 1,579 | 2,287 |  |  |  |  |  |  |  |  | 85 |  |  |  |
Amount paid to transfer ownership and responsibility |  |  |  |  |  |  |  |  |  |  |  |  | 30 |  |  |  |
Nuclear fuel storage costs incurred as a result of the DOE's failure to accept spent nuclear fuel |  |  |  |  |  |  |  |  |  |  |  |  | 55 |  |  |  |
Litigation settlement, gross |  |  |  |  |  |  |  |  |  |  |  |  |  | 120 |  |  |
Proposed recovery of regulatory asset |  |  |  |  |  |  |  |  |  |  |  |  | 85 |  |  |  |
Proposed refund of spent nuclear fuel disposal costs collected |  |  |  |  |  |  |  |  |  |  |  |  | 23 |  |  |  |
Authorized Refund Of Spent Nuclear Fuel Disposal Costs Collected |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 23 |  |
Remaining Portion Of Litigation Settlement |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 |  |
Renewable energy grant received | 69 |  | 69 |  |  |  |  |  |  |  |  |  |  |  |  | 69 |
Recorded liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 68
Energy Optimization Incentive Requested for Exceeding 2012 Savings Targets |  |  |  | 17 |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized Recovery |  |  |  |  |  |  |  |  |  | 16 |  |  |  |  |  |  |
Regulatory asset |  |  |  |  |  |  |  |  |  |  |  | 17 |  |  |  |  |
Requested recovery |  |  |  |  |  |  |  |  |  |  | $ 17 |  |  |  |  |  |

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- Definition The annual rate increase authorized by the MPSC. + References No definition available. + Details
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- Definition The annual rate increase requested. + References No definition available. + Details
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- Definition The amount the MPSC authorized collection from customers. + References No definition available. + Details
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- Definition The amount of spent nuclear fuel disposal costs incurred and collected from customers through rates that the MPSC has authorized for refund + References No definition available. + Details
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- Definition Nuclear fuel storage costs incurred as a result of the DOE's failure to accept spent nuclear fuel. + References No definition available. + Details
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- Definition The portion of the settlement proceeds requested to use as recovery for regulatory assets. + References No definition available. + Details
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- Definition The amount of spent nuclear fuel disposal costs incurred and collected from customers through rates that have been proposed to refund. + References No definition available. + Details
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- Definition The rate of return on equity requested. + References No definition available. + Details
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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 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 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 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 Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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