Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,801	$ 2,111
Depreciation and amortization		238	222
Income (loss) from equity method investees		4	4
Interest charges		106	101
Income tax expense (benefit)		74	100
Net income available to common stockholders		164	202
Plant, property, and equipment, gross		19,334		$ 18,943
Investments in equity method investees		64		64
Total Assets	[1]	20,037		20,299
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,723	2,028
Depreciation and amortization		237	220
Interest charges		67	65
Income tax expense (benefit)		82	110
Net income available to common stockholders		172	215
Plant, property, and equipment, gross		19,165		18,797
Total Assets	[1]	18,422		18,635
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,013	1,033
Net income available to common stockholders		91	94
Plant, property, and equipment, gross	[2]	13,331		13,059
Total Assets	[2]	12,743		12,660
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,013	1,033
Net income available to common stockholders		91	94
Plant, property, and equipment, gross	[2]	13,331		13,059
Total Assets	[2]	12,744		12,660
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		710	995
Net income available to common stockholders		81	121
Plant, property, and equipment, gross	[2]	5,819		5,723
Total Assets	[2]	5,624		5,912
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		710	995
Net income available to common stockholders		81	121
Plant, property, and equipment, gross	[2]	5,819		5,723
Total Assets	[2]	5,624		5,912
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		48	60
Net income available to common stockholders		6	7
Plant, property, and equipment, gross		159		120
Total Assets		261		270
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue		30	23
Net income available to common stockholders		(14)	$ (20)
Plant, property, and equipment, gross		25		41
Total Assets		1,409		1,457
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Plant, property, and equipment, gross		15		15
Total Assets		$ 54		$ 63

[1] CMS Energy and Consumers changed the reporting of debt issuance costs on their consolidated balance sheets in accordance with ASU 2015-03, Simplifying the Presentation of Debt Issuance Costs, as of January 1, 2016, and retrospectively adjusted prior-period amounts for comparability. For further details on the implementation of this standard, see Note 1, New Accounting Standards.

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