Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,486	$ 1,430	$ 4,947	$ 5,421
Net Income Attributable to CMS Energy		148	94	417	381
Plant, property, and equipment, gross		18,547		18,547		$ 17,721
Total Assets		19,452		19,452		19,185
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,417	1,359	4,726	5,128
Net Income Available to Common Stockholders		160	119	458	448
Plant, property, and equipment, gross		18,400		18,400		17,580
Total Assets		17,977		17,977		17,847
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,233	1,153	3,273	3,428
Net Income Attributable to CMS Energy		166	128	342	326
Plant, property, and equipment, gross	[1]	12,803		12,803		12,230
Total Assets	[1]	11,828		11,828		11,582
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,233	1,153	3,273	3,428
Net Income Available to Common Stockholders		166	128	342	326
Plant, property, and equipment, gross	[1]	12,803		12,803		12,230
Total Assets	[1]	11,828		11,828		11,582
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		184	206	1,453	1,699
Net Income Attributable to CMS Energy		(7)	(9)	115	121
Plant, property, and equipment, gross	[1]	5,582		5,582		5,335
Total Assets	[1]	5,546		5,546		5,391
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		184	206	1,453	1,699
Net Income Available to Common Stockholders		(7)	(9)	115	121
Plant, property, and equipment, gross	[1]	5,582		5,582		5,335
Total Assets	[1]	5,546		5,546		5,391
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		43	51	148	235
Net Income Attributable to CMS Energy		3	(7)	10	(3)
Plant, property, and equipment, gross		121		121		115
Total Assets		267		267		231
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue		26	20	73	59
Net Income Attributable to CMS Energy		(14)	$ (18)	(50)	(63)
Plant, property, and equipment, gross		41		41		41
Total Assets		1,811		1,811		1,981
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue					1
Net Income Available to Common Stockholders		1		1	$ 1
Plant, property, and equipment, gross		15		15		15
Total Assets		$ 603		$ 603		$ 874

[1] Amounts include a portion of Consumers' other common assets attributable to both the electric and gas utility businesses.