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Regulatory Matters - (Narrative) (Details) $ in Millions | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Aug. 31, 2023 USD ($) | Jan. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Jun. 30, 2022 USD ($) | Dec. 31, 2023 USD ($) facility | Mar. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Mar. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2016 unit | Dec. 31, 2015 unit | Dec. 31, 2013 USD ($) | Nov. 30, 2023 USD ($) | Sep. 30, 2023 USD ($) | Jun. 30, 2023 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Incentive revenue |  |  |  |  | $ 7,462 |  | $ 8,596 |  | $ 7,329 |  |  |  |  |  |
Regulatory assets |  |  | $ 3,595 |  | 3,683 |  | 3,595 |  |  |  |  |  |  |  |
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Incentive revenue |  |  |  |  | 7,166 |  | 8,151 |  | 7,021 |  |  |  |  |  |
Regulatory assets |  |  | 3,595 |  | 3,683 |  | 3,595 |  |  |  |  |  |  |  |
Regulatory liability |  |  | 3,900 |  | 3,950 |  | 3,900 |  |  |  |  |  |  |  |
Purchased and interchange power |  |  |  |  | 1,331 |  | 1,867 |  | 1,599 |  |  |  |  |  |
Cost of gas sold |  |  |  |  | 897 |  | 1,243 |  | 726 |  |  |  |  |  |
Consumers Energy Company | Voluntary refund mechanism |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability |  |  | 22 |  |  |  | 22 |  |  |  |  |  |  |  |
Consumers Energy Company | Reserve for customer refunds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability |  |  |  |  | 15 |  |  |  |  |  |  |  |  |  |
Consumers Energy Company | Contributions to assistance programs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability |  |  |  |  | $ 10 |  |  |  |  |  |  |  |  |  |
Consumers Energy Company | Renewable energy grant |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from government grant |  |  |  |  |  |  |  |  |  |  |  | $ 69 |  |  |
Consumers Energy Company | MGP sites |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of former MGPs | facility |  |  |  |  | 23 |  |  |  |  |  |  |  |  |  |
Regulatory asset collection period |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |
Consumers Energy Company | Gas-Fueled Electric Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units retired | unit |  |  |  |  |  |  |  |  |  |  | 3 |  |  |  |
Consumers Energy Company | Coal-Fueled Electric Generation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units retired | unit |  |  |  |  |  |  |  |  |  | 7 |  |  |  |  |
Consumers Energy Company | J.H. Campbell Generating Units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  |  |  | $ 1,300 |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  | 9.00% |  |  |  |  |  |  |  |  |  |  |
PSCR underrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSCR underrecoveries |  |  | 401 |  | $ 0 |  | 401 |  |  |  |  |  |  |  |
Purchased and interchange power |  |  |  |  |  |  | 2,500 |  | $ 2,100 |  |  |  |  |  |
Over (under) recovery for gas fuel and power supply costs authorized |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7 |
Over (under) recovery for gas fuel and power supply costs requested |  |  |  |  |  | $ (404) |  |  |  |  |  |  |  |  |
PSCR underrecoveries | Consumers Energy Company | Revision of Prior Period, Adjustment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery for gas fuel and power supply costs requested |  |  |  |  |  |  |  |  |  |  |  |  | $ (401) |  |
Energy Waste Reduction Plan Incentive | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized recovery collection |  |  |  |  |  |  |  |  |  |  |  |  | $ 55 |  |
Incentive revenue |  |  |  |  | 58 |  | $ 55 |  |  |  |  |  |  |  |
Regulatory assets |  |  |  |  | $ 58 |  |  |  |  |  |  |  |  |  |
Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  | 9.90% |  |  |  |  |  |  |  |  |  |  |  |  |
Additional annual rate increase authorized |  | $ 155 |  |  |  |  |  |  |  |  |  |  |  |  |
Surcharge for the recovery of excess distribution investments |  | $ 6 |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized | 9.90% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional annual rate increase authorized | $ 95 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested annual rate increase |  |  | $ 212 |  |  |  |  |  |  |  |  |  |  |  |
Requested annual rate increase, as a percent |  |  | 10.25% |  |  |  |  |  |  |  |  |  |  |  |
GCR underrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery for gas fuel and power supply costs authorized |  |  |  |  |  | (9) |  |  |  |  |  |  |  |  |
Over (under) recovery for gas fuel and power supply costs requested |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (15)
Cost of gas sold |  |  |  |  |  | $ 1,100 |  | $ 700 |  |  |  |  |  |  |

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