Financings And Capitalization (Revolving Credit Facilities) (Details)	3 Months Ended
	Mar. 31, 2017 USD ($)
Revolving Credit Facilities May 27, 2021 [Member] | CMS Energy [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 27, 2021	[1]
Amount of Facility	$ 550,000,000	[1]
Letters of Credit Outstanding	1,000,000	[1]
Amount Available	549,000,000	[1]
Average borrowings	$ 85,000,000
Weighted average interest rate	2.02%
Revolving Credit Facilities May 27, 2021 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 27, 2021
Amount of Facility	$ 650,000,000
Letters of Credit Outstanding	7,000,000
Amount Available	$ 643,000,000
Revolving Credit Facilities November 23, 2018 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	Nov. 23, 2018	[2]
Amount of Facility	$ 250,000,000	[2]
Amount Available	$ 250,000,000	[2]
Revolving Credit Facilities May 9, 2018 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 09, 2018	[2]
Amount of Facility	$ 30,000,000	[2]
Letters of Credit Outstanding	$ 30,000,000	[2]

[1] During the three months ended March 31, 2017, CMS Energy's average borrowings totaled $85 million with a weighted-average interest rate of 2.02 percent. Obligations under this facility are secured by Consumers common stock.

[2] Obligations under this facility are secured by first mortgage bonds of Consumers.