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Regulatory Matters (Narrative) (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jul. 31, 2020 USD ($) | Jul. 31, 2019 USD ($) | Jan. 31, 2019 USD ($) | Oct. 31, 2018 USD ($) | Aug. 31, 2018 USD ($) | Jul. 31, 2018 USD ($) | Jun. 30, 2018 USD ($) | May 31, 2018 USD ($) | Mar. 31, 2018 USD ($) | Oct. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2018 USD ($) site | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2018 USD ($) site | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) site | Dec. 31, 2015 site | Dec. 31, 2013 USD ($) | Dec. 31, 2019 USD ($) | Nov. 30, 2018 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,829 | $ 1,599 | $ 1,492 | $ 1,953 | $ 1,778 | $ 1,527 | $ 1,449 | $ 1,829 | $ 6,873 | $ 6,583 | $ 6,399 |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  |  |  | 155 |  |  |  | 80 |  |  |  | 155 | 80 |  |  |  |  |
Regulatory liability, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  | 3,681 |  |  |  | 3,715 |  |  |  | 3,681 | 3,715 |  |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  | 1,743 |  |  |  | 1,764 |  |  |  | 1,743 | 1,764 |  |  |  |  |
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 1,712 | $ 1,502 | 1,395 | 1,855 | 1,686 | $ 1,437 | $ 1,362 | $ 1,737 | $ 6,464 | 6,222 | 6,064 |  |  |  |
Number of units retired | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  |  |  | 155 |  |  |  | 80 |  |  |  | $ 155 | 80 |  |  |  |  |
Regulatory liability, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  | 3,681 |  |  |  | 3,715 |  |  |  | 3,681 | 3,715 |  |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  | 1,743 |  |  |  | 1,764 |  |  |  | 1,743 | 1,764 |  |  |  |  |
Purchased and interchange power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,587 | 1,491 | 1,486 |  |  |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 819 | 730 | $ 693 |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  | 31 |  |  |  |  |  |  |  | 31 |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 34 | 31 |  |  |  |  |
Gas Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  |  | $ (49) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  |  |  |  |  | $ 83 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case Net Of TCJA Impact | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  | $ 60 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  | $ (113) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  |  | 72 |  | $ 66 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  |  | $ 58 |  |  |  | $ 173 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  |  | 10.75% |  |  |  | 10.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  | $ 44 |  |  |  |  |  |  | $ 148 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase self-implemented |  |  |  |  |  |  |  |  |  | $ 130 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  | $ 11 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  |  |  |  | $ 178 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  |  |  |  | 10.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  |  | $ 60 |  |  | $ 145 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amended requested rate change |  |  |  |  |  | 10.00% |  |  | 10.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSCR overrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchased and interchange power |  |  |  |  |  |  | 1,900 |  | $ 1,900 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery authorized by the MPSC |  |  |  |  |  |  | 12 |  | $ 32 |  |  |  |  |  | 12 | $ 32 |  |  |  |  |  |  |  |  |  |  |
GCR overrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery authorized by the MPSC |  |  |  |  |  |  | 1 | $ 2 |  |  |  |  |  |  | $ 1 |  |  |  |  |  |  |  |  |  |  |  |
Cost of gas sold |  |  |  |  |  |  | $ 600 | $ 500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Manufactured Gas Plant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 142 |  |  |  |  | 142 |  |  |  |  |
Gas Storage Inventory Adjustments | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset collection period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  | 10 |  |  |  | $ 4 | 10 |  |  |  |  |
Scenario, Forecast | Energy Waste Reduction Plan Incentive | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Requested recovery/collection |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 34 |
Scenario, Forecast | Gas Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized | $ 10 | $ 9 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Renewable energy grant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from government grant |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 69 |  |
Regulatory liability, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  | 54 |  |  |  | 56 |  |  |  | 54 | 56 |  |  |  |  |
Revenue subject to refund tax reform rate change | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 31
Revenue subject to refund tax reform rate change | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  |  |  | 70 |  |  |  |  |  |  |  | 70 |  |  |  |  |  |
Income Taxes, Net | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,600 |  |  |  |  | $ 1,600 |  |  |  |  |
Income Taxes, Net | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, noncurrent |  |  |  | 400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes, Net | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, noncurrent |  |  |  | 1,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, noncurrent |  |  |  | $ 1,700 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes Not Subject To Normalization | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets, noncurrent |  |  |  | $ 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes Not Subject To Normalization | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset collection period |  |  |  | 44 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Taxes Not Subject To Normalization | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset collection period |  |  |  | 27 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Taxes Not Related To Plant Assets | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, noncurrent |  |  |  | $ 200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability remaining book life |  |  |  | 15 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue Subject To Refund Other | Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  |  |  |  | $ 36 |  |  |  |  |  |  |  | $ 36 |  |  |  |  |  |
Manufactured Gas Plant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of former MGPs | site |  |  |  |  |  |  |  |  |  |  |  |  | 23 |  |  |  |  |  |  |  | 23 |  |  |  |  |  |
Regulatory asset collection period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  | $ 133 |  |  |  |  |  |  |  | $ 133 |  |  |  |  |  |
Subsequent Event | Electric Rate Case Net Of TCJA Impact | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  | $ 89 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  | $ (24) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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