Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,449	$ 1,371	$ 3,278	$ 3,172
Net Income Attributable to CMS Energy		92	124	291	288
Plant, property, and equipment, gross		21,628		21,628		$ 21,010
Total Assets		21,867		21,867		21,622
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,362	1,293	3,099	3,016
Net income available to common stockholder		103	131	314	303
Plant, property, and equipment, gross		21,451		21,451		20,838
Total Assets		20,205		20,205		19,946
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,077	1,022	2,113	2,035
Net Income Attributable to CMS Energy		94	113	218	204
Plant, property, and equipment, gross	[1]	14,937		14,937		14,540
Total Assets	[1]	13,772		13,772		13,429
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,077	1,022	2,113	2,035
Net income available to common stockholder		94	113	218	204
Plant, property, and equipment, gross	[1]	14,937		14,937		14,540
Total Assets	[1]	13,774		13,774		13,430
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		285	271	986	981
Net Income Attributable to CMS Energy		9	18	96	99
Plant, property, and equipment, gross	[1]	6,499		6,499		6,283
Total Assets	[1]	6,393		6,393		6,446
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		285	271	986	981
Net income available to common stockholder		9	18	96	99
Plant, property, and equipment, gross	[1]	6,499		6,499		6,283
Total Assets	[1]	6,393		6,393		6,446
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		55	49	114	97
Net Income Attributable to CMS Energy		7	3	19	9
Plant, property, and equipment, gross		161		161		157
Total Assets		270		270		269
Other reconciling items [Member]
Segment Reporting Information [Line Items]
Operating Revenue		32	29	65	59
Net Income Attributable to CMS Energy		(18)	$ (10)	(42)	$ (24)
Plant, property, and equipment, gross		31		31		30
Total Assets		1,432		1,432		1,478
Other reconciling items [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Plant, property, and equipment, gross		15		15		15
Total Assets		$ 38		$ 38		$ 70

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