Financings And Capitalization (Revolving Credit Facilities) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($)
Revolving Credit Facilities May 27, 2020 [Member] | CMS Energy [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 27, 2020	[1]
Amount of Facility	$ 550	[1]
Amount Borrowed		[1]
Letters of Credit Outstanding	$ 1	[1]
Amount Available	549	[1]
Average borrowings	$ 10
Weighted average interest rate	1.68%
Revolving Credit Facilities May 27, 2020 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 27, 2020	[2]
Amount of Facility	$ 650	[2]
Amount Borrowed		[2]
Letters of Credit Outstanding	$ 7	[2]
Amount Available	$ 643	[2]
Revolving Credit Facilities November 23, 2017 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	Nov. 23, 2017	[2]
Amount of Facility	$ 250	[2]
Amount Borrowed		[2]
Letters of Credit Outstanding		[2]
Amount Available	$ 250	[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	[2]
Amount Borrowed		[2]
Letters of Credit Outstanding	$ 30	[2]
Amount Available		[2]

[1] During the three months ended March 31, 2016, CMS Energy's average borrowings totaled $10 million with a weighted-average interest rate of 1.68 percent. Obligations under this facility are secured by Consumers common stock.

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