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Contingencies and Commitments (Contingencies And Commitments) (Details) $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2020 USD ($) | May 31, 2020 USD ($) | Dec. 31, 2021 USD ($) site | Sep. 30, 2021 USD ($) | 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 ($) site | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  |  | $ 2,259,000 |  |  |  | $ 2,653,000 |  |  |  | $ 2,259,000 |  | $ 2,653,000 |  |
Operating Revenue |  |  | 2,033,000 | $ 1,725,000 | $ 1,558,000 | $ 2,013,000 | 1,727,000 | $ 1,507,000 | $ 1,382,000 | $ 1,802,000 | 7,329,000 |  | 6,418,000 |  | $ 6,624,000
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  |  | 2,259,000 |  |  |  | 2,653,000 |  |  |  | 2,259,000 |  | 2,653,000 |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  | 726,000 |  | 568,000 |  | 754,000
Plant additions |  |  |  |  |  |  |  |  |  |  | 2,400,000 |  | 2,000,000 |  |
Maintenance and other operating expenses |  |  |  |  |  |  |  |  |  |  | (1,531,000) |  | (1,224,000) |  | (1,275,000)
Operating Revenue |  |  |  |  |  |  |  |  |  |  | 7,021,000 |  | 6,189,000 |  | $ 6,376,000
Consumers Energy Company | Manufactured Gas Plant |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory assets |  |  | 112,000 |  |  |  | $ 120,000 |  |  |  | 112,000 |  | $ 120,000 |  |
Consumers Energy Company | GCR underrecoveries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of gas sold |  |  |  |  |  |  |  |  |  |  |  | $ 400,000 |  | $ 500,000 |
Bay Harbor |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | $ 45,000 |  |  |  |  |  |  |  | $ 45,000 |  |  |  |
Discounted projected costs rate |  |  | 4.34% |  |  |  |  |  |  |  | 4.34% |  |  |  |
Accrual for environmental loss contingencies, inflation rate |  |  | 1.00% |  |  |  |  |  |  |  | 1.00% |  |  |  |
Remaining undiscounted obligation amount |  |  | $ 57,000 |  |  |  |  |  |  |  | $ 57,000 |  |  |  |
CERCLA Liability | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | 3,000 |  |  |  |  |  |  |  | 3,000 |  |  |  |
CERCLA Liability | Minimum | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 3,000 |  |  |  |  |  |  |  | 3,000 |  |  |  |
CERCLA Liability | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 8,000 |  |  |  |  |  |  |  | 8,000 |  |  |  |
Manufactured Gas Plant | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | $ 57,000 |  |  |  |  |  |  |  | $ 57,000 |  |  |  |
Discounted projected costs rate |  |  | 2.57% |  |  |  |  |  |  |  | 2.57% |  |  |  |
Accrual for environmental loss contingencies, inflation rate |  |  | 2.50% |  |  |  |  |  |  |  | 2.50% |  |  |  |
Remaining undiscounted obligation amount |  |  | $ 61,000 |  |  |  |  |  |  |  | $ 61,000 |  |  |  |
Number of former MGPs | site |  |  | 23 |  |  |  |  |  |  |  | 23 |  |  |  |
Regulatory asset collection period |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |
Electric Utility | NREPA | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | $ 2,000 |  |  |  |  |  |  |  | $ 2,000 |  |  |  |
Electric Utility | NREPA | Minimum | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 2,000 |  |  |  |  |  |  |  | 2,000 |  |  |  |
Electric Utility | NREPA | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 4,000 |  |  |  |  |  |  |  | 4,000 |  |  |  |
Gas Utility | NREPA | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | 1,000 |  |  |  |  |  |  |  | 1,000 |  |  |  |
Gas Utility | NREPA | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | 3,000 |  |  |  |  |  |  |  | 3,000 |  |  |  |
Equatorial Guinea Tax Claim |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Foreign government tax claim on sale |  |  | 152,000 |  |  |  |  |  |  |  | 152,000 |  |  |  |
Civil Case, Consumers V. MPSC Staff | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Civil penalty |  | $ 10 |  |  |  |  |  |  |  |  |  |  |  |  |
Ray Compressor Station | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant additions |  |  |  |  |  |  |  |  |  |  | 17,000 |  |  |  |
Insurance recoveries |  |  | $ 13,000 |  |  |  |  |  |  |  | 13,000 |  |  |  |
Ray Compressor Station | Consumers Energy Company | Insurance Recoveries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction to plant, property and equipment |  |  |  |  |  |  |  |  |  |  | 6,000 |  |  |  |
Maintenance and other operating expenses |  |  |  |  |  |  |  |  |  |  | 3,000 |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  | $ 4,000 |  |  |  |
Ray Compressor Station | Consumers Energy Company | GCR underrecoveries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of gas sold | $ 7,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |

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