Financings And Capitalization (Revolving Credit Facilities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Revolving Credit Facilities December 20, 2018 [Member] | CMS Energy [Member]
Line of Credit Facility [Line Items]
Expiration Date	Dec. 20, 2018	[1]
Amount of Facility	$ 550	[1]
Amount Borrowed	100	[1]
Letters of Credit Outstanding	3	[1]
Amount Available	447	[1]
Average borrowings	68
Weighted average interest rate	1.42%
Revolving Credit Facilities December 20, 2018 [Member] | Consumers Energy Company [Member]
Line of Credit Facility [Line Items]
Expiration Date	Dec. 20, 2018	[2]
Amount of Facility	650	[2]
Amount Borrowed		[2]
Letters of Credit Outstanding	10	[2]
Amount Available	640	[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, 2015, CMS Energy’s average borrowings totaled $68 million with a weighted-average interest rate of 1.42 percent. Obligations under this facility are secured by Consumers common stock.

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