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Contingencies and Commitments (Contingencies And Commitments) (Details) $ in Thousands | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
May 30, 2020 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2020 USD ($) lawsuit site | Mar. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jan. 31, 2019 USD ($)
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
ARO liability incurred |  |  | $ 65,000 |  | $ 55,000 |  |  |
Regulatory assets |  |  | 2,653,000 |  | 2,489,000 |  |  |
Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
ARO liability incurred |  |  | 46,000 |  | 55,000 |  |  |
Regulatory assets |  |  | 2,653,000 |  | 2,489,000 |  |  |
Cost of gas sold |  |  | 568,000 |  | 754,000 |  | $ 819,000 |
Plant additions |  |  | 2,000,000 |  | 2,000,000 |  |  |
Consumers Energy Company | GCR underrecoveries |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Cost of gas sold |  |  |  | $ 500,000 |  | $ 600,000 |  |
Bay Harbor |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | $ 45,000 |  |  |  |  |
Discounted projected costs rate |  |  | 4.34% |  |  |  |  |
Accrual for environmental loss contingencies, inflation rate |  |  | 1.00% |  |  |  |  |
Remaining undiscounted obligation amount |  |  | $ 57,000 |  |  |  |  |
CERCLA Liability | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | 3,000 |  |  |  |  |
CERCLA Liability | Minimum | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 3,000 |  |  |  |  |
CERCLA Liability | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 8,000 |  |  |  |  |
Manufactured Gas Plant | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | $ 56,000 |  |  |  |  |
Discounted projected costs rate |  |  | 2.57% |  |  |  |  |
Accrual for environmental loss contingencies, inflation rate |  |  | 2.50% |  |  |  |  |
Remaining undiscounted obligation amount |  |  | $ 61,000 |  |  |  |  |
Number of former MGPs | site |  |  | 23 |  |  |  |  |
Regulatory asset collection period |  |  | 10 years |  |  |  |  |
Electric Utility | NREPA | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | $ 2,000 |  |  |  |  |
Electric Utility | NREPA | Minimum | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 2,000 |  |  |  |  |
Electric Utility | NREPA | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  | 4,000 |  |  |  |  |
Gas Utility | NREPA | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | 1,000 |  |  |  |  |
Gas Utility | NREPA | Maximum | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies |  |  | 3,000 |  |  |  |  |
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] |  |  |  |  |  |  |  |
Estimated current litigation liability |  |  |  |  | $ 30,000 |  |  |
MCV PPA | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Remediation and other response activity costs |  |  |  |  |  |  |  | $ 270,000
Underwater cables Straits of Mackinac | Consumers Energy Company |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
ARO liability incurred |  | $ 5,000 |  |  |  |  |  |
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 |  |  |  |  |
Ray Compressor Station | Consumers Energy Company | GCR underrecoveries |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Cost of gas sold |  |  |  |  |  | $ 7,000 |  |

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