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Contingencies And Commitments (Guarantees) (Details) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2015 USD ($) $ / MWh MW | Dec. 31, 2015 USD ($) $ / MWh MW | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($)
Guarantor Obligations [Line Items] |  |  |  |  |
Interest expense reduction |  |  | $ (14) | $ (17) | $ (16)
Interest income |  |  | $ 12 | 5 | 3
Consumers Energy Company [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Expiration Date | [1] |  | Indefinite |  |
Maximum obligation | [1] | $ 30 | $ 30 |  |
Interest expense reduction |  |  | (2) | (10) | (11)
Interest income |  |  | 11 | 4 | 2
Consumers Energy Company [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Tax examination refund |  | 37 | 37 |  |
Interest expense reduction |  | 12 |  |  |
Interest income |  | 6 |  |  |
PPE reduction resulting from tax refund |  | 19 |  |  |
Reduction of income tax expense |  | 5 |  |  |
Consumers Energy Company [Member] | Refund Of Taxes Paid Receivable [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Tax examination refund |  | 19 | 19 |  |
Consumers Energy Company [Member] | Refund Of Interest Paid Receivable [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Tax examination refund |  | 12 | 12 |  |
Consumers Energy Company [Member] | Interest Receivable [Member] | Settlement with Taxing Authority [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Tax examination refund |  | 6 | $ 6 |  |
Guarantees [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Expiration Date | [1] |  | Indefinite |  |
Maximum obligation | [1] | 51 | $ 51 |  |
Indemnity Obligations From Asset Sales And Other Agreements [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Expiration Date | [2] |  | Indefinite |  |
Maximum obligation | [2] | 143 | $ 143 |  |
Carrying Amount | [2] | 7 | 7 |  |
Tax And Other Indemnity Obligations [Member] | Consumers Energy Company [Member] | Maximum [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Carrying Amount |  | 1 | 1 |  |
MCV PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Purchase Obligations Total |  | 3,003 | 3,003 |  |
Purchase Obligations Due in Year One |  | 335 | 335 |  |
Purchase Obligations Due in Year Two |  | 345 | 345 |  |
Purchase Obligations Due in Year Three |  | 277 | 277 |  |
Purchase Obligations Due in Year Four |  | 321 | 321 |  |
Purchase Obligations Due in Year Five |  | 296 | 296 |  |
Purchase Obligations Due After Year Five |  | $ 1,429 | $ 1,429 |  |
Term of Unrecorded Unconditional Purchase Obligations |  |  | 35 years |  |
Unrecorded Unconditional Purchase Obligations, Minimum Quantity Required | MW |  | 1,240 | 1,240 |  |
Unrecorded Unconditional Purchase Obligation Capacity Charge Per Mwh | $ / MWh |  | 10.14 | 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 |  |  | $ 282 | 300 | 278
Palisades PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Purchase Obligations Total |  | $ 2,327 | 2,327 |  |
Purchase Obligations Due in Year One |  | 342 | 342 |  |
Purchase Obligations Due in Year Two |  | 352 | 352 |  |
Purchase Obligations Due in Year Three |  | 363 | 363 |  |
Purchase Obligations Due in Year Four |  | 374 | 374 |  |
Purchase Obligations Due in Year Five |  | 387 | 387 |  |
Purchase Obligations Due After Year Five |  | 509 | 509 |  |
Unrecorded Unconditional Purchase Obligation, Purchases |  |  | $ 352 | 302 | 338
Unrecorded Unconditional Purchase Obligations, Maximum Quantity | MW |  |  | 798 |  |
Related Parties PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Purchase Obligations Total |  | 977 | $ 977 |  |
Purchase Obligations Due in Year One |  | 82 | 82 |  |
Purchase Obligations Due in Year Two |  | 82 | 82 |  |
Purchase Obligations Due in Year Three |  | 82 | 82 |  |
Purchase Obligations Due in Year Four |  | 85 | 85 |  |
Purchase Obligations Due in Year Five |  | 87 | 87 |  |
Purchase Obligations Due After Year Five |  | 559 | 559 |  |
Other PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Purchase Obligations Total |  | 3,640 | 3,640 |  |
Purchase Obligations Due in Year One |  | 240 | 240 |  |
Purchase Obligations Due in Year Two |  | 248 | 248 |  |
Purchase Obligations Due in Year Three |  | 247 | 247 |  |
Purchase Obligations Due in Year Four |  | 223 | 223 |  |
Purchase Obligations Due in Year Five |  | 225 | 225 |  |
Purchase Obligations Due After Year Five |  | 2,457 | 2,457 |  |
Unrecorded Unconditional Purchase Obligation, Purchases |  |  | 347 | $ 354 | $ 345
PPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Purchase Obligations Total |  | 9,947 | 9,947 |  |
Purchase Obligations Due in Year One |  | 999 | 999 |  |
Purchase Obligations Due in Year Two |  | 1,027 | 1,027 |  |
Purchase Obligations Due in Year Three |  | 969 | 969 |  |
Purchase Obligations Due in Year Four |  | 1,003 | 1,003 |  |
Purchase Obligations Due in Year Five |  | 995 | 995 |  |
Purchase Obligations Due After Year Five |  | 4,954 | 4,954 |  |
Other Purchase Obligations [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Purchase Obligations Total |  | 2,200 | 2,200 |  |
Purchase Obligations Due in Year One |  | 904 | 904 |  |
Purchase Obligations Due in Year Two |  | 580 | 580 |  |
Purchase Obligations Due in Year Three |  | 251 | 251 |  |
Purchase Obligations Due in Year Four |  | 111 | 111 |  |
Purchase Obligations Due in Year Five |  | 63 | 63 |  |
Purchase Obligations Due After Year Five |  | 291 | 291 |  |
Other Purchase Obligations [Member] | Consumers Energy Company [Member] |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |
Purchase Obligations Total |  | 1,908 | 1,908 |  |
Purchase Obligations Due in Year One |  | 870 | 870 |  |
Purchase Obligations Due in Year Two |  | 551 | 551 |  |
Purchase Obligations Due in Year Three |  | 224 | 224 |  |
Purchase Obligations Due in Year Four |  | 83 | 83 |  |
Purchase Obligations Due in Year Five |  | 34 | 34 |  |
Purchase Obligations Due After Year Five |  | $ 146 | $ 146 |  |
[1] | At Consumers, this obligation comprises a guarantee provided to the DOE in connection with a settlement agreement regarding damages resulting from the DOE'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 DOE and CMS Energy's 1994 guarantee of non-recourse revenue bonds issued by Genesee. For additional details on this guarantee, see Note 19, 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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