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Regulatory Matters (Narrative) (Details) $ in Millions |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Mar. 31, 2019 USD ($) | Oct. 31, 2019 USD ($) | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Apr. 30, 2019 USD ($) | Jan. 31, 2019 USD ($) | Nov. 30, 2018 USD ($) | Oct. 31, 2018 USD ($) | May 31, 2018 USD ($) | Dec. 31, 2019 USD ($) coal_fueled_electric_generating_unit site | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Dec. 31, 2019 USD ($) coal_fueled_electric_generating_unit site | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 site | Dec. 31, 2015 site | Dec. 31, 2013 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | $ 1,795 | $ 1,546 | $ 1,445 | $ 2,059 | $ 1,829 | $ 1,599 | $ 1,492 | $ 1,953 | $ 6,845 | $ 6,873 | $ 6,583 |  |  |
Regulatory liability, noncurrent |  |  |  |  |  |  |  |  |  | 3,742 |  |  |  | 3,681 |  |  |  | 3,742 | 3,681 |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  | 87 |  |  |  | 155 |  |  |  | 87 | 155 |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  | 2,489 |  |  |  | 1,743 |  |  |  | 2,489 | 1,743 |  |  |  |
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  | 1,670 | 1,429 | 1,334 | 1,943 | 1,712 | $ 1,502 | $ 1,395 | $ 1,855 | $ 6,376 | 6,464 | 6,222 |  |  |
Number of units retired | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  |  |  |
Regulatory liability, noncurrent |  |  |  |  |  |  |  |  |  | 3,742 |  |  |  | 3,681 |  |  |  | $ 3,742 | 3,681 |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  | 87 |  |  |  | 155 |  |  |  | 87 | 155 |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  | $ 2,489 |  |  |  | 1,743 |  |  |  | 2,489 | 1,743 |  |  |  |
Purchased and interchange power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,470 | 1,587 | 1,491 |  |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 754 | 819 | $ 730 |  |  |
Costs of coal-fueled electric generating units to be retired | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units | coal_fueled_electric_generating_unit |  |  |  |  |  |  |  |  |  | 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 |  |  |  |  |  |  |  |  |  | $ 34 |  |  |  |  |  |  |  | $ 34 |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 34 | 34 |  |  |  |
Requested recovery/collection |  |  |  |  |  |  |  |  |  | 34 |  |  |  |  |  |  |  | $ 34 |  |  |  |  |
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  | $ (113) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case Net Of TCJA Impact | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  | 89 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  |  |  |  | $ (24) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  |  |  | $ 58 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  |  |  | 10.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  |  |  |  | $ 44 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate Case | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  | $ 144 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested |  |  |  |  |  |  | $ 229 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity requested |  |  |  |  |  |  | 10.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase requested, amended |  |  |  |  | $ 204 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate of return on equity authorized |  |  | 9.90% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Rate TCJA Adjustment | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual rate increase authorized |  |  | $ (13) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSCR overrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchased and interchange power | $ 2,000 | $ 1,900 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery authorized by the MPSC | $ (31) | $ 32 |  |  |  |  |  |  |  |  |  |  | $ (31) |  |  |  |  |  |  |  |  |  |
GCR underrecoveries | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Over (under) recovery authorized by the MPSC |  |  | 1 | $ (18) |  |  |  |  |  |  | 1 | $ (18) |  |  |  |  |  |  |  |  |  |  |
Cost of gas sold |  |  | 600 | $ 600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Manufactured Gas Plant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  |  |  |  |  | 133 |  |  |  |  | 133 |  |  |  |
Gas Storage Inventory Adjustments | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset collection period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |
Regulatory assets, noncurrent |  |  |  |  |  |  |  |  |  | 3 |  |  |  | 4 |  |  |  | $ 3 | 4 |  |  |  |
Renewable energy grant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, noncurrent |  |  |  |  |  |  |  |  |  | 52 |  |  |  | 54 |  |  |  | 52 | 54 |  |  |  |
Proceeds from government grant |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 69
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approved temporary bill credit |  |  | 32 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
TCJA reserve for refund | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, noncurrent |  |  | $ 62 |  |  |  |  |  |  | 0 | $ 62 |  |  | 35 |  |  |  | 0 | 35 |  |  |  |
Regulatory liabilities, current |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  | $ 98 |  |  |  | $ 0 | $ 98 |  |  |  |
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 |  |  |  |  |  |  |  |  |  | $ 130 |  |  |  |  |  |  |  | $ 130 |  |  |  |  |

X
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