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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jul. 31, 2020 | Jul. 31, 2019 | Oct. 25, 2018 | Aug. 31, 2018 | Jul. 31, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Oct. 31, 2017 | Sep. 30, 2017 | Mar. 31, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017 | May 31, 2018
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  | $ 165 |  | $ 165 |  | $ 80 |
Regulatory liabilities, noncurrent |  |  |  |  |  |  |  |  |  |  | 3,745 |  | 3,745 |  | 3,715 |
Regulatory assets |  |  |  |  |  |  |  |  |  |  | 1,655 |  | 1,655 |  | 1,764 |
Revenue |  |  |  |  |  |  |  |  |  |  | 1,599 | $ 1,527 | 5,044 | $ 4,805 |  |
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  | 165 |  | 165 |  | 80 |
Regulatory liabilities, noncurrent |  |  |  |  |  |  |  |  |  |  | 3,745 |  | 3,745 |  | 3,715 |
Regulatory assets |  |  |  |  |  |  |  |  |  |  | 1,655 |  | 1,655 |  | 1,764 |
Revenue |  |  |  |  |  |  |  |  |  |  | 1,502 | $ 1,437 | 4,752 | $ 4,536 |  |
Income Taxes, Net | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  |  |  |  |  |  |  | 1,600 |  | 1,600 |  |  |
Income Taxes Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  |  |  |  |  |  |  | 1,700 |  | 1,700 |  |  |
Income Taxes Not Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  |  |  |  |  |  |  |  |  |  | 300 |  | 300 |  |  |
Taxes Not Related To Plant Assets | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  |  |  |  |  |  |  | 200 |  | 200 |  |  |
Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  |  |  |  | $ 173 |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  |  |  |  | 10.50% |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  |  |  |  |  | $ 148 |  |  |  |  |  |  |
Annual rate increase self-implemented |  |  |  |  |  |  |  | $ 130 |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  | $ 72 | $ 66 |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |
Electric Rate Case | Revenue Subject to Refund - Other | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  | 36 |  | 36 |  |  |
Gas Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  |  | $ 178 |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  |  | 10.50% |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  | $ 60 |  | $ 145 |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  | $ 11 |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |
Authorized amended return on equity |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase 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 |  | 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 |  | 1,200 |  |  |
Gas Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  |  |  | $ 83 |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  | $ (49) |  |  |  |  |  |  |  |  |  |
Authorized amended return on equity |  |  |  |  |  |  | 10.75% |  |  |  |  |  |  |  |  |
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 |  | 31 |  |  |
Gas Rate Case Tax Reform Rate Change | Income Taxes, Net | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, noncurrent |  |  |  |  |  |  |  |  |  |  | $ 400 |  | $ 400 |  |  |
Energy Waste Reduction Plan | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested recovery/collection |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 31
Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 31 |
Scenario, Forecast | Gas Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized | $ 10 | $ 9 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | Taxes Not Related To Plant Assets | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability remaining life (in years) |  |  | 15 years |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | 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) |  |  | 36 years |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | 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 |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | 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 |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | 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 |  |  |  |  |  |  |  |  |  |  |  |  |

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