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Contingencies And Commitments (Contingencies And Commitments) (Details) $ in Thousands |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jan. 31, 2019 USD ($) | May 30, 2020 USD ($) | Jan. 31, 2019 USD ($) | Sep. 30, 2020 USD ($) site | Sep. 30, 2019 USD ($) | Sep. 30, 2020 USD ($) lawsuit site | Sep. 30, 2019 USD ($) | Dec. 31, 2019 USD ($) lawsuit | Mar. 31, 2020 USD ($)
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Regulatory assets |  |  |  | $ 2,745,000 |  | $ 2,745,000 |  | $ 2,489,000 |
Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Regulatory assets |  |  |  | 2,745,000 |  | 2,745,000 |  | $ 2,489,000 |
Cost of gas sold |  |  |  | 33,000 | $ 32,000 | 383,000 | $ 537,000 |  |
Bay Harbor |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Accrual for obligations for environmental remediation |  |  |  | $ 44,000 |  | $ 44,000 |  |  |
Discounted projected costs rate |  |  |  | 4.34% |  | 4.34% |  |  |
Accrual for environmental loss contingencies, inflation rate |  |  |  | 1.00% |  | 1.00% |  |  |
Remaining undiscounted obligation amount |  |  |  | $ 55,000 |  | $ 55,000 |  |  |
Electric Utility | NREPA | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Accrual for obligations for environmental remediation |  |  |  | 3,000 |  | 3,000 |  |  |
Electric Utility | NREPA | Minimum | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  |  | 3,000 |  | 3,000 |  |  |
Electric Utility | NREPA | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  |  | 4,000 |  | 4,000 |  |  |
Electric Utility | CERCLA Liability | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Accrual for obligations for environmental remediation |  |  |  | 3,000 |  | 3,000 |  |  |
Electric Utility | CERCLA Liability | Minimum | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  |  | 3,000 |  | 3,000 |  |  |
Electric Utility | CERCLA Liability | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  |  | 8,000 |  | 8,000 |  |  |
Gas Utility | NREPA | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Accrual for obligations for environmental remediation |  |  |  | 1,000 |  | 1,000 |  |  |
Gas Utility | NREPA | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  |  | 3,000 |  | 3,000 |  |  |
Gas Utility | Manufactured Gas Plant | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Accrual for obligations for environmental remediation |  |  |  | $ 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 |  |  |  | $ 62,000 |  | $ 62,000 |  |  |
Number of former MGPs | site |  |  |  | 23 |  | 23 |  |  |
Authorized recovery, collection period |  |  |  |  |  | 10 years |  |  |
Regulatory assets |  |  |  | $ 122,000 |  | $ 122,000 |  |  |
Equatorial Guinea Tax Claim |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Foreign government tax claim on sale |  |  |  |  |  | $ 152,000 |  |  |
Class Action Lawsuits |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Number of lawsuits | lawsuit |  |  |  |  |  | 4 |  |  |
Individual Lawsuits |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Number of lawsuits | lawsuit |  |  |  |  |  | 1 |  |  |
Gas Index Price Reporting Litigation |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Number of lawsuits | lawsuit |  |  |  |  |  |  |  | 2 |
Estimated litigation liability |  |  |  |  |  |  |  | $ 30,000 |
MCV PPA | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Foreign government tax claim on sale |  |  | $ 270,000 |  |  |  |  |  |
Underwater cables Straits of Mackinac | Minimum | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Asset retirement obligation |  |  |  |  |  |  |  |  | $ 5,000
Civil Case, Consumers V. MPSC Staff | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Civil penalty settlement |  | $ 10 |  |  |  |  |  |  |
Ray Compressor Station | Consumers Energy Company |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |
Cost of gas sold | $ 7,000 |  |  |  |  |  |  |  |
Capital expenditures |  |  |  |  |  | $ 17,000 |  |  |

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