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Financings And Capitalization (Revolving Credit Facilities) (Details)
9 Months Ended
Sep. 30, 2017
USD ($)
Revolving Credit Facilities May 27, 2022 [Member] | CMS Energy [Member]  
Line of Credit Facility [Line Items]  
Expiration Date May 27, 2022 [1],[2]
Amount of Facility $ 550,000,000 [1],[2]
Letters of Credit Outstanding 1,000,000 [1],[2]
Amount Available 549,000,000 [1],[2]
Average borrowings $ 28,000,000
Weighted average interest rate 2.02%
Revolving Credit Facilities May 27, 2022 [Member] | Consumers Energy Company [Member]  
Line of Credit Facility [Line Items]  
Expiration Date May 27, 2022 [2],[3]
Amount of Facility $ 650,000,000 [2],[3]
Letters of Credit Outstanding 7,000,000 [2],[3]
Amount Available $ 643,000,000 [2],[3]
Revolving Credit Facilities November 23, 2018 [Member] | Consumers Energy Company [Member]  
Line of Credit Facility [Line Items]  
Expiration Date Nov. 23, 2018 [3]
Amount of Facility $ 250,000,000 [3]
Amount Available $ 250,000,000 [3]
Revolving Credit Facilities September 9, 2019 [Member] | Consumers Energy Company [Member]  
Line of Credit Facility [Line Items]  
Expiration Date Sep. 09, 2019 [3],[4]
Amount of Facility $ 30,000,000 [3],[4]
Letters of Credit Outstanding $ 30,000,000 [3],[4]
[1] During the nine months ended September 30, 2017, CMS Energy's average borrowings totaled $28 million with a weighted-average interest rate of 2.02 percent. Obligations under this facility are secured by Consumers common stock.
[2] In May 2017, the expiration date of this revolving credit agreement was extended from May 2021 to May 2022.
[3] Obligations under this facility are secured by first mortgage bonds of Consumers.
[4] In June 2017, the expiration date of this letter of credit reimbursement agreement was extended from May 2018 to September 2019.