Financings And Capitalization (Revolving Credit Facilities) (Details)	3 Months Ended
	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.