Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,587	$ 1,486	$ 4,759	$ 4,947
Net Income Attributable to CMS Energy		186	148	474	417
Plant, property, and equipment, gross		20,698		20,698		$ 18,943
Total Assets	[1]	20,842		20,842		20,299
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,498	1,417	4,514	4,726
Net income (loss) available to common stockholder		195	160	498	458
Plant, property, and equipment, gross		20,528		20,528		18,797
Total Assets	[1]	18,980		18,980		18,635
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,313	1,233	3,348	3,273
Net Income Attributable to CMS Energy		191	166	395	342
Plant, property, and equipment, gross	[2]	14,396		14,396		13,059
Total Assets	[2]	12,892		12,892		12,660
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,313	1,233	3,348	3,273
Net income (loss) available to common stockholder		191	166	395	342
Plant, property, and equipment, gross	[2]	14,396		14,396		13,059
Total Assets	[2]	12,892		12,892		12,660
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		185	184	1,166	1,453
Net Income Attributable to CMS Energy		3	(7)	102	115
Plant, property, and equipment, gross	[2]	6,117		6,117		5,723
Total Assets	[2]	6,033		6,033		5,912
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		185	184	1,166	1,453
Net income (loss) available to common stockholder		3	(7)	102	115
Plant, property, and equipment, gross	[2]	6,117		6,117		5,723
Total Assets	[2]	6,033		6,033		5,912
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		59	43	156	148
Net Income Attributable to CMS Energy		8	3	17	10
Plant, property, and equipment, gross		158		158		120
Total Assets		273		273		270
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue		30	26	89	73
Net Income Attributable to CMS Energy		(16)	(14)	(40)	(50)
Plant, property, and equipment, gross		27		27		41
Total Assets		1,644		1,644		1,457
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Net income (loss) available to common stockholder		1	$ 1	1	$ 1
Plant, property, and equipment, gross		15		15		15
Total Assets		$ 55		$ 55		$ 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.