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Regulatory Matters (Narrative) (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2019 USD ($) coal_fueled_electric_generating_unit | Apr. 30, 2019 USD ($) | Jan. 31, 2019 USD ($) | Nov. 30, 2018 USD ($) | Oct. 31, 2018 USD ($) | Jun. 30, 2018 USD ($) | May 31, 2018 USD ($) | Sep. 30, 2019 USD ($) coal_fueled_electric_generating_unit | Sep. 30, 2018 USD ($) | Sep. 30, 2019 USD ($) coal_fueled_electric_generating_unit | Sep. 30, 2018 USD ($) | Dec. 31, 2018 USD ($) | Aug. 31, 2019 USD ($) | May 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current | $ 72 |  |  |  |  |  |  | $ 72 |  | $ 72 |  | $ 155 |  |
Regulatory liabilities, noncurrent | 3,754 |  |  |  |  |  |  | 3,754 |  | 3,754 |  | 3,681 |  |
Regulatory assets | 2,367 |  |  |  |  |  |  | 2,367 |  | 2,367 |  | 1,743 |  |
Revenue |  |  |  |  |  |  |  | 1,546 | $ 1,599 | 5,050 | $ 5,044 |  |  |
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current | 72 |  |  |  |  |  |  | 72 |  | 72 |  | 155 |  |
Regulatory liabilities, noncurrent | 3,754 |  |  |  |  |  |  | 3,754 |  | 3,754 |  | 3,681 |  |
Regulatory assets | 2,367 |  |  |  |  |  |  | 2,367 |  | 2,367 |  | 1,743 |  |
Revenue |  |  |  |  |  |  |  | 1,429 | $ 1,502 | 4,706 | $ 4,752 |  |  |
Income Taxes, Net | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  | $ 1,600 |  |  |  |  |  |  |  |  |
Income Taxes Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  | 1,700 |  |  |  |  |  |  |  |  |
Income Taxes Not Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  |  |  |  | 300 |  |  |  |  |  |  |  |  |
Taxes Not Related To Plant Assets | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  | $ 200 |  |  |  |  |  |  |  |  |
Regulatory liability remaining life (in years) |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |
TCJA Reserve For Refund | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent | 62 |  |  |  |  |  |  | 62 |  | 62 |  |  |  |
Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase (decrease) authorized |  |  | $ (24) |  |  | $ 72 |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  | 10.00% |  |  | 10.00% |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  | $ 58 |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  | 10.75% |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  | $ 44 |  |  |  |  |  |  |  |  |
Electric Rate Case | Revenue Subject to Refund - Other | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  |  |  | $ 34 |
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase (decrease) authorized |  |  | $ (113) |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case Tax Reform Rate Change | Revenue Subject to Refund - Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  |  | 70 |  |
Electric Rate Case Tax Reform Rate Change | Income Taxes, Net | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  | $ 1,200 |  |  |  |  |  |  |  |  |
Approved interim bill credit | 32 |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case Tax Reform Rate Change | Income Taxes Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability remaining life (in years) |  |  |  |  | 27 years |  |  |  |  |  |  |  |  |
Electric Rate Case Tax Reform Rate Change | Income Taxes Not Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset remaining life (in years) |  |  |  |  | 27 years |  |  |  |  |  |  |  |  |
Electric Rate Case Net Of TCJA Impact | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase (decrease) authorized |  |  | $ 89 |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase (decrease) authorized | $ 144 |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized | 9.90% |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  | $ 229 |  |  |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  | 10.75% |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  | $ 204 |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate TCJA Adjustment | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase (decrease) authorized | $ (13) |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case Tax Reform Rate Change | Revenue Subject to Refund - Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  | $ 31 |  |  |  |  |  |  |  |  |  |
Gas Rate Case Tax Reform Rate Change | Income Taxes, Net | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  | $ 400 |  |  |  |  |  |  |  |  |
Gas Rate Case Tax Reform Rate Change | Income Taxes Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability remaining life (in years) |  |  |  |  | 44 years |  |  |  |  |  |  |  |  |
Gas Rate Case Tax Reform Rate Change | Income Taxes Not Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset remaining life (in years) |  |  |  |  | 44 years |  |  |  |  |  |  |  |  |
Energy Waste Reduction Plan Incentive | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested recovery/collection |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 34
Revenue |  |  |  |  |  |  |  |  |  |  |  | $ 34 |  |
Coal-Fueled Electric Generating Units to be Retired | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets | $ 657 |  |  |  |  |  |  | $ 657 |  | $ 657 |  |  |  |
Number of units | coal_fueled_electric_generating_unit | 2 |  |  |  |  |  |  | 2 |  | 2 |  |  |  |

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