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Contingencies And Commitments (Guarantees) (Details) $ in Millions | 3 Months Ended
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Mar. 31, 2018 USD ($)
Guarantees [Member] |  |
Guarantees And Other Contingencies [Line Items] |  |
Guarantee Description | Guarantees | [1]
Expiration Date | Indefinite | [1]
Maximum obligation | $ 42 | [1]
Guarantees [Member] | Consumers Energy Company [Member] |  |
Guarantees And Other Contingencies [Line Items] |  |
Guarantee Description | Guarantee | [1]
Expiration Date | Indefinite | [1]
Maximum obligation | $ 30 | [1]
Indemnity Obligations From Stock And Asset Sales Agreements [Member] |  |
Guarantees And Other Contingencies [Line Items] |  |
Guarantee Description | Indemnity obligations from stock and asset sales agreements | [2]
Expiration Date | Indefinite | [2]
Maximum obligation | $ 153 | [2]
Carrying Amount | 7 | [2]
Tax And Other Indemnity Obligations [Member] | Consumers Energy Company [Member] |  |
Guarantees And Other Contingencies [Line Items] |  |
Carrying Amount | $ 1 |
[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.
[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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- Definition Guarantees And Other Contingencies [Line Items] + References No definition available. + Details
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- Definition The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248 + Details
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- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248 + Details
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- Definition Describes how and under what circumstances or in connection with which transaction the guarantee or each group of similar guarantees was given and the objective of the guarantee. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248 + Details
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- Definition Describe the approximate term of the guarantee or each group of similar guarantees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248 + Details
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