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Regulatory Matters (Narrative) (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2021 USD ($) coal_fueled_electric_generating_unit site | Jul. 31, 2021 USD ($) | Mar. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) coal_fueled_electric_generating_unit site | Sep. 30, 2021 USD ($) | Jun. 30, 2021 USD ($) | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Sep. 30, 2020 USD ($) | Jun. 30, 2020 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2021 USD ($) coal_fueled_electric_generating_unit site | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2016 site | Dec. 31, 2015 site | Dec. 31, 2013 USD ($) | Jan. 31, 2022 USD ($) | Oct. 31, 2021 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  | $ 2,033 | $ 1,725 | $ 1,558 | $ 2,013 | $ 1,727 | $ 1,507 | $ 1,382 | $ 1,802 | $ 7,329 |  | $ 6,418 |  | $ 6,624 |  |  |  |  |
Regulatory liabilities, current | $ 146 |  |  | 146 |  |  |  | 151 |  |  |  | 146 |  | 151 |  |  |  |  |  |  |
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  | $ 7,021 |  | 6,189 |  | 6,376 |  |  |  |  |
Number of units retired | site |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  |  |  |  |  |  |  |
Regulatory liabilities, current | $ 146 |  |  | $ 146 |  |  |  | 151 |  |  |  | $ 146 |  | 151 |  |  |  |  |  |  |
Reduction in depreciation expense |  |  |  |  |  |  |  |  |  |  |  | 1,077 |  | 1,023 |  | 975 |  |  |  |  |
Plant additions |  |  |  |  |  |  |  |  |  |  |  | 2,400 |  | 2,000 |  |  |  |  |  |  |
Purchased and interchange power |  |  |  |  |  |  |  |  |  |  |  | 1,599 |  | 1,454 |  | 1,470 |  |  |  |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  | $ 726 |  | 568 |  | 754 |  |  |  |  |
Costs of coal-fueled electric generating units to be retired | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Assets, Number Of Units | coal_fueled_electric_generating_unit | 2 |  |  | 2 |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Coal-Fueled Electric Generation | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units retired | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7 |  |  |  |
Gas-Fueled Electric Generation | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units retired | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |  |
Energy Waste Reduction Plan Incentive | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized recovery collection |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 42
Revenue |  |  |  |  |  |  |  |  |  |  |  | $ 46 |  | 42 |  |  |  |  |  |  |
Requested recovery/collection | $ 46 |  |  | $ 46 |  |  |  |  |  |  |  | 46 |  |  |  |  |  |  |  |  |
Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  | $ 225 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  | 10.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  | $ 201 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized | $ 27 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized | 9.90% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction in depreciation expense | $ (27) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment charge | 4 |  |  |  |  |  |  |  |  |  |  | 41 |  |  |  |  |  |  |  |  |
Assessment of probable loss | 11 |  |  | 11 |  |  |  |  |  |  |  | 11 |  |  |  |  |  |  |  |  |
Plant additions |  |  |  |  |  |  |  |  |  |  |  | $ 23 |  |  |  |  |  |  |  |  |
Held-for-sale fleet assets | 15 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case | Consumers Energy Company | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Recommended disallowed costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 11 |
PSCR overrecoveries/underrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchased and interchange power |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,800 |  | 1,900 |  |  |  |  |
Over (under) recovery authorized by the MPSC |  |  |  |  |  |  |  | (4) |  |  |  |  |  | (4) |  | $ 18 |  |  |  |  |
GCR underrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery authorized by the MPSC |  |  | $ 1 |  |  |  | $ 1 |  |  |  | $ 6 |  | $ 1 |  | $ 6 |  |  |  |  |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  |  | $ 400 |  | $ 500 |  |  |  |  |  |
Renewable energy grant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from government grant |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 69 |  |
Income Taxes Subject To Normalization | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability remaining book life |  |  |  |  |  |  |  |  |  |  |  | 44 years |  |  |  |  |  |  |  |  |
Income Taxes Subject To Normalization | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability remaining book life |  |  |  |  |  |  |  |  |  |  |  | 27 years |  |  |  |  |  |  |  |  |
Reserve for customer refunds | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current | 2 |  |  | 2 |  |  |  | 28 |  |  |  | $ 2 |  | 28 |  |  |  |  |  |  |
Voluntary transmission asset sale gain share | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current | $ 0 |  |  | $ 0 |  |  |  | $ 14 |  |  |  | $ 0 |  | $ 14 |  |  |  |  |  |  |
Manufactured Gas Plant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of former MGPs | site | 23 |  |  | 23 |  |  |  |  |  |  |  | 23 |  |  |  |  |  |  |  |  |
Regulatory asset collection period |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |

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