Financings And Capitalization (Revolving Credit Facilities) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Revolving Credit Facilities May 27, 2021 [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 27, 2021	[1],[2]
Amount of Facility	$ 550	[1],[2]
Amount Borrowed		[1],[2]
Letters of Credit Outstanding	1	[1],[2]
Amount Available	549	[1],[2]
Revolving Credit Facilities May 27, 2021 [Member] | CMS Energy [Member]
Line of Credit Facility [Line Items]
Average borrowings	$ 3
Weighted average interest rate	1.68%
Revolving Credit Facilities May 27, 2021 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 27, 2021	[2],[3]
Amount of Facility	$ 650	[2],[3]
Amount Borrowed		[2],[3]
Letters of Credit Outstanding	7	[2],[3]
Amount Available	$ 643	[2],[3]
Revolving Credit Facilities November 23, 2017 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	Nov. 23, 2018	[3],[4]
Amount of Facility	$ 250	[3],[4]
Amount Borrowed		[3],[4]
Amount Available	$ 250	[3],[4]
Revolving Credit Facilities May 9, 2018 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	May 09, 2018	[3]
Amount of Facility	$ 30	[3]
Amount Borrowed		[3]
Letters of Credit Outstanding	$ 30	[3]

[1] During the year ended December 31, 2016, CMS Energy's average borrowings totaled $3 million with a weighted-average interest rate of 1.68 percent. Obligations under this facility are secured by Consumers common stock.

[2] In May 2016, the expiration date of this revolving credit agreement was extended from 2020 to 2021.

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

[4] In November 2016, the expiration date of this revolving credit agreement was extended from 2017 to 2018.