Reportable Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,758		$ 1,430	$ 1,468	$ 2,523	$ 1,736		$ 1,445	$ 1,406	$ 1,979	$ 7,179		$ 6,566		$ 6,253
Depreciation and amortization											685		628		598
Income (loss) from equity method investees											15		13		17
Interest charges											407		398		389
Income tax expense (benefit)											250		302		245
Net Income Attributable to CMS Energy	96		94	83	204	102		126	80	144	477		452		382
Plant, property, and equipment, gross	17,721					16,184					17,721		16,184		15,592
Investments in equity method investees	61	[1]				59	[1]				61	[1]	59	[1]	57	[1]
Total Assets	19,185					17,416					19,185		17,416		17,131
Capital Expenditures											1,616	[2]	1,408	[2]	1,266	[2]
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,672		1,359	1,387	2,382	1,674		1,386	1,342	1,919	6,800		6,321		6,013
Depreciation and amortization											678		622		592
Interest charges											250		245		244
Income tax expense (benefit)											306		346		297
Net Income Available to Common Stockholders	117		119	108	221	119		152	99	162	565		532		437
Plant, property, and equipment, gross	17,580					16,044					17,580		16,044		15,456
Total Assets	17,847					16,179					17,847		16,179		16,275
Capital Expenditures											1,612		1,403		1,261
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue											4,436		4,173		4,031
Depreciation and amortization											522		484		459
Interest charges											181		179		179
Income tax expense (benefit)											211		242		227
Net Income Attributable to CMS Energy											384		363		325
Plant, property, and equipment, gross	12,230					11,186					12,230		11,186		11,041
Total Assets	11,582	[3]				10,487	[3]				11,582	[3]	10,487	[3]	10,423	[3]
Capital Expenditures											1,139		996		921
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue											4,436		4,173		4,031
Depreciation and amortization											522		484		459
Interest charges											181		179		179
Income tax expense (benefit)											211		242		227
Net Income Available to Common Stockholders											384		363		325
Plant, property, and equipment, gross	12,230					11,186					12,230		11,186		11,041
Total Assets	11,582	[3]				10,487	[3]				11,582	[3]	10,487	[3]	10,423	[3]
Capital Expenditures											1,139		996		921
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue											2,363		2,148		1,982
Depreciation and amortization											156		138		133
Interest charges											67		64		63
Income tax expense (benefit)											95		104		70
Net Income Attributable to CMS Energy											179		168		110
Plant, property, and equipment, gross	5,335					4,843					5,335		4,843		4,400
Total Assets	5,391	[3]				4,784	[3]				5,391	[3]	4,784	[3]	5,016	[3]
Capital Expenditures											473		407		340
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue											2,363		2,148		1,982
Depreciation and amortization											156		138		133
Interest charges											67		64		63
Income tax expense (benefit)											95		104		70
Net Income Available to Common Stockholders											179		168		110
Plant, property, and equipment, gross	5,335					4,843					5,335		4,843		4,400
Total Assets	5,391	[3]				4,784	[3]				5,391	[3]	4,784	[3]	5,016	[3]
Capital Expenditures											473	[2]	407	[2]	340	[2]
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue											299		181		183
Depreciation and amortization											4		3		4
Income (loss) from equity method investees											15	[1]	13	[1]	17	[1]
Income tax expense (benefit)											(1)		(4)		(1)
Net Income Attributable to CMS Energy											(1)		2		16
Plant, property, and equipment, gross	115					115					115		115		113
Investments in equity method investees	58					57					58		57		55
Total Assets	231					332					231		332		181
Capital Expenditures											3	[2]	1	[2]	1	[2]
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue											81		64		57
Depreciation and amortization											3		3		2
Interest charges											159		155		147
Income tax expense (benefit)											(55)		(40)		(51)
Net Income Attributable to CMS Energy											(85)		(81)		(69)
Plant, property, and equipment, gross	41					40					41		40		38
Investments in equity method investees	3					2					3		2		2
Total Assets	1,981					1,813					1,981		1,813		1,511
Capital Expenditures											1		4		4
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue											1
Interest charges											2		2		2
Net Income Available to Common Stockholders											2		1		2
Plant, property, and equipment, gross	15					15					15		15		15
Total Assets	$ 874					$ 908					$ 874		$ 908		$ 836

[1] Consumers had no significant equity method investments.

[2] Amounts include purchase of capital lease additions. Amounts also include a portion of Consumers’ capital expenditures for plant and equipment attributable to both the electric and gas utility businesses.

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