Financings And Capitalization (Revolving Credit Facilities) (Details) $ in Millions	12 Months Ended
	Dec. 31, 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	[1],[2]
Amount Borrowed		[1],[2]
Letters of Credit Outstanding	6	[1],[2]
Amount Available	544	[1],[2]
Average borrowings	$ 21
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	[2],[3]
Amount Borrowed		[2],[3]
Letters of Credit Outstanding	7	[2],[3]
Amount Available	$ 643	[2],[3]
Revolving Credit Facilities November 23, 2019 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	Nov. 23, 2019	[3],[4]
Amount of Facility	$ 250	[3],[4]
Amount Borrowed		[3],[4]
Letters of Credit Outstanding	20	[3],[4]
Amount Available	$ 230	[3],[4]
Revolving Credit Facilities September 9, 2019 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	Sep. 09, 2019	[3],[5]
Amount of Facility	$ 30	[3],[5]
Amount Borrowed		[3],[5]
Letters of Credit Outstanding	$ 30	[3],[5]

[1] During the year ended December 31, 2017, CMS Energy's average borrowings totaled $21 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 these facilities are secured by first mortgage bonds of Consumers.

[4] In November 2017, the expiration date of this revolving credit agreement was extended from November 2018 to November 2019.

[5] In June 2017, the expiration date of this letter of credit reimbursement agreement was extended from May 2018 to September 2019.