Financings And Capitalization (Revolving Credit Facilities) (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2015		Sep. 30, 2014
Revolving Credit Facilities May 27, 2020 [Member] | CMS Energy [Member]
Line of Credit Facility [Line Items]
Expiration Date	[1]	May 27, 2020
Amount of Facility	[1]	$ 550
Amount Borrowed	[1]
Letters of Credit Outstanding	[1]	$ 3
Amount Available	[1]	547
Average borrowings		$ 61
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	[2]	May 27, 2020
Amount of Facility		$ 650	[2]	$ 650
Amount Borrowed	[2]
Letters of Credit Outstanding	[2]	$ 10
Amount Available	[2]	$ 640
Revolving Credit Facilities May 9, 2018 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	[2]	May 09, 2018
Amount of Facility	[2]	$ 30
Amount Borrowed	[2]
Letters of Credit Outstanding	[2]	$ 30
Amount Available	[2]

[1] During the six months ended June 30, 2015, CMS Energy's average borrowings totaled $61 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.