Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,527	$ 1,587	$ 4,805	$ 4,759
Net Income Attributable to CMS Energy		172	186	463	474
Plant, property, and equipment, gross		21,966		21,966		$ 21,010
Total Assets		22,120		22,120		21,622
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,437	1,498	4,536	4,514
Net income available to common stockholder		181	195	495	498
Plant, property, and equipment, gross		21,784		21,784		20,838
Total Assets		20,380		20,380		19,946
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,247	1,313	3,360	3,348
Net Income Attributable to CMS Energy		176	191	394	395
Plant, property, and equipment, gross	[1]	15,056		15,056		14,540
Total Assets	[1]	13,639		13,639		13,429
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,247	1,313	3,360	3,348
Net income available to common stockholder		176	191	394	395
Plant, property, and equipment, gross	[1]	15,056		15,056		14,540
Total Assets	[1]	13,640		13,640		13,430
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		190	185	1,176	1,166
Net Income Attributable to CMS Energy		5	3	101	102
Plant, property, and equipment, gross	[1]	6,713		6,713		6,283
Total Assets	[1]	6,701		6,701		6,446
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		190	185	1,176	1,166
Net income available to common stockholder		5	3	101	102
Plant, property, and equipment, gross	[1]	6,713		6,713		6,283
Total Assets	[1]	6,701		6,701		6,446
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		58	59	172	156
Net Income Attributable to CMS Energy		8	8	27	17
Plant, property, and equipment, gross		164		164		157
Total Assets		280		280		269
Other reconciling items [Member]
Segment Reporting Information [Line Items]
Operating Revenue		32	30	97	89
Net Income Attributable to CMS Energy		(17)	(16)	(59)	(40)
Plant, property, and equipment, gross		33		33		30
Total Assets		1,500		1,500		1,478
Other reconciling items [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Net income available to common stockholder			$ 1		$ 1
Plant, property, and equipment, gross		15		15		15
Total Assets		$ 39		$ 39		$ 70

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