Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,350	$ 1,468	$ 3,461	$ 3,991
Net Income Attributable to CMS Energy		67	83	269	287
Plant, property, and equipment, gross		18,217		18,217		$ 17,721
Total Assets		19,238		19,238		19,185
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,281	1,387	3,309	3,769
Net Income Available to Common Stockholders		83	108	298	329
Plant, property, and equipment, gross		18,074		18,074		17,580
Total Assets		17,867		17,867		17,847
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,007	1,051	2,040	2,275
Net Income Attributable to CMS Energy		82	98	176	198
Plant, property, and equipment, gross	[1]	12,597		12,597		12,230
Total Assets	[1]	11,906		11,906		11,582
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,007	1,051	2,040	2,275
Net Income Available to Common Stockholders		82	98	176	198
Plant, property, and equipment, gross	[1]	12,597		12,597		12,230
Total Assets	[1]	11,906		11,906		11,582
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		274	335	1,269	1,493
Net Income Attributable to CMS Energy		1	9	122	130
Plant, property, and equipment, gross	[1]	5,462		5,462		5,335
Total Assets	[1]	5,309		5,309		5,391
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		274	335	1,269	1,493
Net Income Available to Common Stockholders		1	9	122	130
Plant, property, and equipment, gross	[1]	5,462		5,462		5,335
Total Assets	[1]	5,309		5,309		5,391
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		45	62	105	184
Net Income Attributable to CMS Energy			2	7	4
Plant, property, and equipment, gross		118		118		115
Total Assets		267		267		231
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue		24	20	47	39
Net Income Attributable to CMS Energy		(16)	(26)	(36)	(45)
Plant, property, and equipment, gross		40		40		41
Total Assets		1,756		1,756		1,981
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue			1		1
Net Income Available to Common Stockholders			$ 1		$ 1
Plant, property, and equipment, gross		15		15		15
Total Assets		$ 652		$ 652		$ 874

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