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Financings And Capitalization (Revolving Credit Facilities) (Details) | 3 Months Ended
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Mar. 31, 2018 USD ($)
Revolving Credit Facilities May 27, 2022 [Member] | Consumers Energy Company [Member] |  |
Line of Credit Facility [Line Items] |  |
Expiration Date | May 27, 2022 | [1]
Amount of Facility | $ 650,000,000 | [1]
Letters of Credit Outstanding | 7,000,000 | [1]
Amount Available | $ 643,000,000 | [1]
Revolving Credit Facilities November 23, 2019 [Member] | Consumers Energy Company [Member] |  |
Line of Credit Facility [Line Items] |  |
Expiration Date | Nov. 23, 2019 | [1]
Amount of Facility | $ 250,000,000 | [1]
Letters of Credit Outstanding | 15,000,000 | [1]
Amount Available | $ 235,000,000 | [1]
Revolving Credit Facilities September 9, 2019 [Member] | Consumers Energy Company [Member] |  |
Line of Credit Facility [Line Items] |  |
Expiration Date | Sep. 09, 2019 | [1]
Amount of Facility | $ 30,000,000 | [1]
Letters of Credit Outstanding | $ 30,000,000 | [1]
CMS Energy [Member] | Revolving Credit Facilities May 27, 2022 [Member] |  |
Line of Credit Facility [Line Items] |  |
Expiration Date | May 27, 2022 | [2]
Amount of Facility | $ 550,000,000 | [2]
Amount Borrowed | 50,000,000 | [2]
Letters of Credit Outstanding | 1,000,000 | [2]
Amount Available | 499,000,000 | [2]
Average borrowings | $ 34,000,000 |
Weighted average interest rate | 2.75% |
[1] | Obligations under this facility are secured by first mortgage bonds of Consumers.
[2] | During the three months ended March 31, 2018, CMS Energy's average borrowings totaled $34 million with a weighted-average interest rate of 2.75 percent. Obligations under this facility are secured by Consumers common stock.

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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
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Balance Type: | credit
Period Type: | instant

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Average amount borrowed under the credit facility during the period. + References No definition available. + Details
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Balance Type: | credit
Period Type: | duration

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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The effective interest rate during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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Balance Type: | credit
Period Type: | instant

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