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Contingencies and Commitments (Guarantees) (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 USD ($) $ / MW $ / MWh MW | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jul. 31, 2020
Variable Interest Entity, Primary Beneficiary | Aviator Wind Class B Membership |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Ownership percentage |  |  |  | 49.00%
Guarantees |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Expiration Date | indefinite |  |  |
Maximum Obligation | $ 30 |  |  |
Carrying Amount | $ 0 |  |  |
Guarantees | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Expiration Date | indefinite |  |  |
Maximum Obligation | $ 30 |  |  |
Carrying Amount | $ 0 |  |  |
Indemnification Agreement From Purchase Of Variable Interest Entity |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Expiration Date | indefinite |  |  |
Maximum Obligation | $ 349 |  |  |
Carrying Amount | $ 0 |  |  |
Indemnity Obligations From Stock And Asset Sales Agreements |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Expiration Date | indefinite |  |  |
Maximum Obligation | $ 153 |  |  |
Carrying Amount | 2 |  |  |
Tax And Other Indemnity Obligations | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Carrying Amount | 1 |  |  |
MCV PPA | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Total | 2,815 |  |  |
2021 | 349 |  |  |
2022 | 340 |  |  |
2023 | 358 |  |  |
2024 | 376 |  |  |
2025 | 329 |  |  |
Beyond 2025 | $ 1,063 |  |  |
PPA minimum quantity required | MW | 1,240 |  |  |
PPA fixed energy charge per MWh, on-peak (in dollars per MWh) | $ / MWh | 6.30 |  |  |
PPA fixed energy charge per MWh, off-peak (in dollars per MWh) | $ / MWh | 6.00 |  |  |
Annual contribution to renewable resources program by counterparty | $ 5 |  |  |
Purchases | $ 298 | $ 318 | $ 353 |
MCV PPA | Consumers Energy Company | Year End Through March 2025 |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
PPA capacity charge per MWh (in dollars per MWh) | $ / MW | 10.14 |  |  |
MCV PPA | Consumers Energy Company | March 2025 Through Termination |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
PPA capacity charge per MWh (in dollars per MWh) | $ / MW | 5.00 |  |  |
Palisades PPA | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Total | $ 517 |  |  |
2021 | 398 |  |  |
2022 | 119 |  |  |
2023 | 0 |  |  |
2024 | 0 |  |  |
2025 | 0 |  |  |
Beyond 2025 | 0 |  |  |
Purchases | 403 | 395 | 375 |
Related-party PPAs | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Total | 318 |  |  |
2021 | 58 |  |  |
2022 | 58 |  |  |
2023 | 58 |  |  |
2024 | 58 |  |  |
2025 | 39 |  |  |
Beyond 2025 | 47 |  |  |
Other PPAs | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Total | 5,248 |  |  |
2021 | 252 |  |  |
2022 | 274 |  |  |
2023 | 315 |  |  |
2024 | 350 |  |  |
2025 | 364 |  |  |
Beyond 2025 | 3,693 |  |  |
Purchases | 327 | $ 336 | $ 350 |
Total PPAs | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Total | 8,898 |  |  |
2021 | 1,057 |  |  |
2022 | 791 |  |  |
2023 | 731 |  |  |
2024 | 784 |  |  |
2025 | 732 |  |  |
Beyond 2025 | 4,803 |  |  |
Other |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Total | 3,179 |  |  |
2021 | 1,391 |  |  |
2022 | 871 |  |  |
2023 | 265 |  |  |
2024 | 199 |  |  |
2025 | 171 |  |  |
Beyond 2025 | 282 |  |  |
Other | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Total | 2,605 |  |  |
2021 | 1,333 |  |  |
2022 | 777 |  |  |
2023 | 207 |  |  |
2024 | 154 |  |  |
2025 | 130 |  |  |
Beyond 2025 | $ 4 |  |  |
Palisades Power Purchase Agreement | Financing Obligation | Consumers Energy Company |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |
Annual average capacity (in MW) | MW | 798 |  |  |

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