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Regulatory Matters (Narrative) (Details) - Consumers Energy Company [Member] - USD ($) $ in Millions | 1 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jan. 31, 2015 | Dec. 31, 2014 | Jul. 31, 2014 | Jun. 30, 2015 | May. 31, 2015
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Energy optimization incentive requested for exceeding savings targets |  |  |  |  | $ 17
Electric Rate Case [Member] |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Annual rate increase requested |  | $ 163 |  |  |
Rate of return on equity requested |  | 10.70% |  |  |
Annual rate increase self-implemented |  |  |  | $ 110 |
Electric Rate Case [Member] | 2016 and 2017 Planned Investments [Member] |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Investment recovery mechanism requested |  | $ 163 |  |  |
Electric Rate Case [Member] | 2018 Planned Investments [Member] |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Investment recovery mechanism requested |  | $ 78 |  |  |
Gas Rate Case [Member] |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Annual rate increase requested |  |  | $ 88 |  |
Annual rate increase authorized | $ 45 |  |  |  |
Rate of return on equity authorized | 10.30% |  |  |  |

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