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Contingencies And Commitments (Guarantees) (Details) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2016 USD ($) | Dec. 31, 2016 USD ($) $ / MWh MW | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
PPE reduction resulting from tax refund |  |  | $ 34 |  |
Income Tax Settlement [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Reduction of income tax expense |  |  | 3 |  |
General Taxes [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Reduction of income tax expense |  |  | $ 3 |  |
Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Expiration Date | [1] |  | Indefinite |  |
Maximum obligation | [1] |  | $ 30 |  |
Consumers Energy Company [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  | $ 60 |  | $ 37 |
Tax refund received |  | 13 |  |  |
Note receivable in 2017 |  | 30 |  |  |
Note receivable, in 2018 |  | 17 |  |  |
Gain (loss) related to tax settlement |  |  | $ 4 |  |
Consumers Energy Company [Member] | Interest Expense [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  |  |  | 12 |
Consumers Energy Company [Member] | Interest Income [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  |  |  | 6 |
Consumers Energy Company [Member] | General Taxes [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  |  |  | 5 |
Consumers Energy Company [Member] | Refund Of Taxes Paid Receivable [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  | 42 |  |  |
Consumers Energy Company [Member] | Refund Of Interest Paid Receivable [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  | 12 |  |  |
Consumers Energy Company [Member] | Interest Receivable [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  | $ 6 |  |  |
Consumers Energy Company [Member] | Plant, Property, And Equipment [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Tax examination refund |  |  |  | 19 |
Guarantees [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Expiration Date | [1] |  | Indefinite |  |
Maximum obligation | [1] |  | $ 48 |  |
Indemnity Obligations From Stock And Asset Sales Agreements [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Expiration Date | [2] |  | Indefinite |  |
Maximum obligation | [2] |  | $ 153 |  |
Carrying Amount | [2] |  | 7 |  |
Tax And Other Indemnity Obligations [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Carrying Amount |  |  | 1 |  |
MCV PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Purchase Obligations Total |  |  | 3,010 |  |
Purchase Obligations Due in Year One |  |  | 326 |  |
Purchase Obligations Due in Year Two |  |  | 331 |  |
Purchase Obligations Due in Year Three |  |  | 330 |  |
Purchase Obligations Due in Year Four |  |  | 344 |  |
Purchase Obligations Due in Year Five |  |  | 325 |  |
Purchase Obligations Due After Year Five |  |  | $ 1,354 |  |
Term of Unrecorded Unconditional Purchase Obligations |  |  | 35 years |  |
Unrecorded Unconditional Purchase Obligations, Minimum Quantity Required | MW |  |  | 1,240 |  |
Unrecorded Unconditional Purchase Obligation Capacity Charge Per Mwh | $ / MWh |  |  | 10.14 |  |
Unrecorded Unconditional Purchase Obligation, Annual Contribution to Renewable Resources Program By Counterparty |  |  | $ 5 |  |
Unrecorded Unconditional Purchase Obligation, Contract Extension Period |  |  | 5 years |  |
Unrecorded Unconditional Purchase Obligation, Purchases |  |  | $ 305 | 282 | $ 300
Palisades PPA [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Unrecorded Unconditional Purchase Obligations, Maximum Quantity | MW |  |  | 798 |  |
Palisades PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Purchase Obligations Total |  |  | $ 1,994 |  |
Purchase Obligations Due in Year One |  |  | 354 |  |
Purchase Obligations Due in Year Two |  |  | 365 |  |
Purchase Obligations Due in Year Three |  |  | 376 |  |
Purchase Obligations Due in Year Four |  |  | 388 |  |
Purchase Obligations Due in Year Five |  |  | 398 |  |
Purchase Obligations Due After Year Five |  |  | 113 |  |
Unrecorded Unconditional Purchase Obligation, Purchases |  |  | $ 363 | 352 | 302
Unrecorded Unconditional Purchase Obligations, Maximum Quantity | MW |  |  | 798 |  |
Related Parties PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Purchase Obligations Total |  |  | $ 899 |  |
Purchase Obligations Due in Year One |  |  | 81 |  |
Purchase Obligations Due in Year Two |  |  | 82 |  |
Purchase Obligations Due in Year Three |  |  | 86 |  |
Purchase Obligations Due in Year Four |  |  | 88 |  |
Purchase Obligations Due in Year Five |  |  | 88 |  |
Purchase Obligations Due After Year Five |  |  | 474 |  |
Other PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Purchase Obligations Total |  |  | 3,453 |  |
Purchase Obligations Due in Year One |  |  | 247 |  |
Purchase Obligations Due in Year Two |  |  | 253 |  |
Purchase Obligations Due in Year Three |  |  | 229 |  |
Purchase Obligations Due in Year Four |  |  | 231 |  |
Purchase Obligations Due in Year Five |  |  | 233 |  |
Purchase Obligations Due After Year Five |  |  | 2,260 |  |
Unrecorded Unconditional Purchase Obligation, Purchases |  |  | 348 | $ 347 | $ 354
PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Purchase Obligations Total |  |  | 9,356 |  |
Purchase Obligations Due in Year One |  |  | 1,008 |  |
Purchase Obligations Due in Year Two |  |  | 1,031 |  |
Purchase Obligations Due in Year Three |  |  | 1,021 |  |
Purchase Obligations Due in Year Four |  |  | 1,051 |  |
Purchase Obligations Due in Year Five |  |  | 1,044 |  |
Purchase Obligations Due After Year Five |  |  | 4,201 |  |
Other Purchase Obligations [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Purchase Obligations Total |  |  | 1,922 |  |
Purchase Obligations Due in Year One |  |  | 931 |  |
Purchase Obligations Due in Year Two |  |  | 376 |  |
Purchase Obligations Due in Year Three |  |  | 187 |  |
Purchase Obligations Due in Year Four |  |  | 132 |  |
Purchase Obligations Due in Year Five |  |  | 32 |  |
Purchase Obligations Due After Year Five |  |  | 264 |  |
Other Purchase Obligations [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantees And Other Contingencies [Line Items] |  |  |  |  |
Purchase Obligations Total |  |  | 1,651 |  |
Purchase Obligations Due in Year One |  |  | 895 |  |
Purchase Obligations Due in Year Two |  |  | 347 |  |
Purchase Obligations Due in Year Three |  |  | 157 |  |
Purchase Obligations Due in Year Four |  |  | 102 |  |
Purchase Obligations Due in Year Five |  |  | 19 |  |
Purchase Obligations Due After Year Five |  |  | $ 131 |  |
[1] | At Consumers, this obligation comprises a guarantee provided to the U.S. Department of Energy in connection with a settlement agreement regarding damages resulting from the department's failure to accept spent nuclear fuel from nuclear power plants formerly owned by Consumers. At CMS Energy, the guarantee obligations comprise Consumers' guarantee to the U.S. Department of Energy and CMS Energy's 1994 guarantee of non-recourse revenue bonds issued by Genesee. For additional details on this guarantee, see Note 20, Variable Interest Entities.
[2] | These obligations arose from stock and asset sale agreements under which CMS Energy or a subsidiary of CMS Energy indemnified the purchaser for losses resulting from various matters, primarily claims related to taxes. CMS Energy believes the likelihood of material loss to be remote for the indemnity obligations not recorded as liabilities.

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