Financings And Capitalization (Revolving Credit Facilities) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 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	$ 3	[1]
Amount Available	547	[1]
Average borrowings	$ 40
Weighted average interest rate	1.43%
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	$ 9	[2]
Amount Available	$ 641	[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 nine months ended September 30, 2015, CMS Energy's average borrowings totaled $40 million with a weighted-average interest rate of 1.43 percent. Obligations under this facility are secured by Consumers common stock.

[2] Obligations under this facility are secured by FMBs of Consumers.