Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,371	$ 1,350	$ 3,172	$ 3,461
Income (loss) from equity method investees		3	1	7	5
Net Income Attributable to CMS Energy		124	67	288	269
Plant, property, and equipment, gross		20,497		20,497		$ 18,943
Investments in equity method investees		66		66		64
Total Assets	[1]	20,463		20,463		20,299
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,293	1,281	3,016	3,309
Net Income Available to Common Stockholders		131	83	303	298
Plant, property, and equipment, gross		20,326		20,326		18,797
Total Assets	[1]	18,702		18,702		18,635
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,022	1,007	2,035	2,040
Net Income Attributable to CMS Energy		113	82	204	176
Plant, property, and equipment, gross	[2]	14,297		14,297		13,059
Total Assets	[2]	12,901		12,901		12,660
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,022	1,007	2,035	2,040
Net Income Available to Common Stockholders		113	82	204	176
Plant, property, and equipment, gross	[2]	14,297		14,297		13,059
Total Assets	[2]	12,902		12,902		12,660
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		271	274	981	1,269
Net Income Attributable to CMS Energy		18	1	99	122
Plant, property, and equipment, gross	[2]	6,014		6,014		5,723
Total Assets	[2]	5,744		5,744		5,912
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		271	274	981	1,269
Net Income Available to Common Stockholders		18	1	99	122
Plant, property, and equipment, gross	[2]	6,014		6,014		5,723
Total Assets	[2]	5,744		5,744		5,912
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		49	45	97	105
Net Income Attributable to CMS Energy		3		9	7
Plant, property, and equipment, gross		160		160		120
Total Assets		267		267		270
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue		29	24	59	47
Net Income Attributable to CMS Energy		(10)	$ (16)	(24)	$ (36)
Plant, property, and equipment, gross		26		26		41
Total Assets		1,551		1,551		1,457
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Plant, property, and equipment, gross		15		15		15
Total Assets		$ 56		$ 56		$ 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.