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Contingencies And Commitments (Guarantees) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2018 USD ($) $ / MW MW | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Guarantees |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Expiration Date | indefinite |  |
Maximum Obligation | $ 39 |  |
Carrying Amount | $ 0 |  |
Guarantees | Consumers Energy Company |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Expiration Date | indefinite |  |
Maximum Obligation | $ 30 |  |
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 | 3 |  |
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 | 3,880 |  |
2019 | 330 |  |
2020 | 318 |  |
2021 | 289 |  |
2022 | 275 |  |
2023 | 279 |  |
Beyond 2023 | $ 2,389 |  |
Term of unrecorded PPA | 35 years |  |
PPA minimum quantity required | MW | 1,240 |  |
PPA capacity charge per MWh (in dollars per MWh) | $ / MW | 10.14 |  |
Annual contribution to renewable resources program by counterparty | $ 5 |  |
Contract extension period | 5 years |  |
Purchases | $ 353 | $ 321 | $ 305
Palisades PPA | Consumers Energy Company |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Total | 1,280 |  |
2019 | 378 |  |
2020 | 388 |  |
2021 | 400 |  |
2022 | 114 |  |
2023 | 0 |  |
Beyond 2023 | 0 |  |
Purchases | $ 375 | 366 | 363
Annual average capacity (in MW) | MW | 798 |  |
Related-party PPAs | Consumers Energy Company |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Total | $ 692 |  |
2019 | 85 |  |
2020 | 85 |  |
2021 | 86 |  |
2022 | 86 |  |
2023 | 87 |  |
Beyond 2023 | 263 |  |
Other PPAs | Consumers Energy Company |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Total | 4,078 |  |
2019 | 256 |  |
2020 | 260 |  |
2021 | 268 |  |
2022 | 269 |  |
2023 | 272 |  |
Beyond 2023 | 2,753 |  |
Purchases | 350 | $ 349 | $ 348
Total PPAs | Consumers Energy Company |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Total | 9,930 |  |
2019 | 1,049 |  |
2020 | 1,051 |  |
2021 | 1,043 |  |
2022 | 744 |  |
2023 | 638 |  |
Beyond 2023 | 5,405 |  |
Other |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Total | 2,341 |  |
2019 | 1,276 |  |
2020 | 405 |  |
2021 | 163 |  |
2022 | 137 |  |
2023 | 117 |  |
Beyond 2023 | 243 |  |
Other | Consumers Energy Company |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |
Total | 2,075 |  |
2019 | 1,237 |  |
2020 | 373 |  |
2021 | 148 |  |
2022 | 124 |  |
2023 | 103 |  |
Beyond 2023 | $ 90 |  |

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