Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,640	$ 1,587	$ 1,371	$ 1,801	$ 1,509	$ 1,486	$ 1,350	$ 2,111	$ 6,399	$ 6,456	$ 7,179
Depreciation and amortization										811	750	685
Income from equity method investees	[1]									13	14	15
Interest charges										435	396	407
Income tax expense (benefit)										273	271	250
Net Income Attributable to CMS Energy		77	186	124	164	106	148	67	202	551	523	477
Plant, property, and equipment, gross		21,010				18,943				21,010	18,943	17,721
Investments in equity method investees	[1]	65				64				65	64	61
Total Assets		21,622				20,299				21,622	20,299	19,143
Capital expenditures	[2]									1,633	1,741	1,616
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,550	1,498	1,293	1,723	1,439	1,417	1,281	2,028	6,064	6,165	6,800
Depreciation and amortization										803	744	678
Interest charges										268	250	250
Income tax expense (benefit)										320	302	306
Net income (loss) available to common stockholder		116	$ 195	$ 131	$ 172	134	$ 160	$ 83	$ 215	614	592	565
Plant, property, and equipment, gross		20,838				18,797				20,838	18,797	17,580
Total Assets		19,946				18,635				19,946	18,635	17,824
Capital expenditures	[2]									1,618	1,694	1,612
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue										4,379	4,249	4,436
Depreciation and amortization										603	567	522
Interest charges										196	178	181
Income tax expense (benefit)										246	224	211
Net Income Attributable to CMS Energy										458	437	384
Plant, property, and equipment, gross		14,540				13,059				14,540	13,059	12,230
Total Assets	[3]	13,429				12,660				13,429	12,660	11,565
Capital expenditures	[2]									1,007	1,136	1,139
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue										4,379	4,249	4,436
Depreciation and amortization										603	567	522
Interest charges										196	178	181
Income tax expense (benefit)										246	224	211
Net income (loss) available to common stockholder										458	437	384
Plant, property, and equipment, gross		14,540				13,059				14,540	13,059	12,230
Total Assets	[3]	13,430				12,660				13,430	12,660	11,565
Capital expenditures	[2]									1,007	1,136	1,139
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue										1,685	1,916	2,363
Depreciation and amortization										200	177	156
Interest charges										72	71	67
Income tax expense (benefit)										74	78	95
Net Income Attributable to CMS Energy										155	154	179
Plant, property, and equipment, gross		6,283				5,723				6,283	5,723	5,335
Total Assets	[3]	6,446				5,912				6,446	5,912	5,385
Capital expenditures	[2]									611	558	473
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue										1,685	1,916	2,363
Depreciation and amortization										200	177	156
Interest charges										72	71	67
Income tax expense (benefit)										74	78	95
Net income (loss) available to common stockholder										155	154	179
Plant, property, and equipment, gross		6,283				5,723				6,283	5,723	5,335
Total Assets	[3]	6,446				5,912				6,446	5,912	5,385
Capital expenditures	[2]									611	558	473
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue										215	190	299
Depreciation and amortization										5	4	4
Income from equity method investees	[1]									13	14	15
Interest charges										1
Income tax expense (benefit)										10	3	(1)
Net Income Attributable to CMS Energy										17	4	(1)
Plant, property, and equipment, gross		157				120				157	120	115
Investments in equity method investees	[1]	62				61				62	61	58
Total Assets		269				270				269	270	231
Capital expenditures	[2]									10	44	3
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue										120	101	81
Depreciation and amortization										3	2	3
Interest charges										166	147	159
Income tax expense (benefit)										(57)	(34)	(55)
Net Income Attributable to CMS Energy										(79)	(72)	(85)
Plant, property, and equipment, gross		30				41				30	41	41
Investments in equity method investees	[1]	3				3				3	3	3
Total Assets		1,478				1,457				1,478	1,457	1,962
Capital expenditures	[2]									5	3	1
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue												1
Interest charges											1	2
Net income (loss) available to common stockholder										1	1	2
Plant, property, and equipment, gross		15				15				15	15	15
Total Assets		$ 70				$ 63				$ 70	$ 63	$ 874

[1] Consumers had no significant equity method investments.

[2] Amounts include purchase of capital lease additions. Amounts also include a portion of Consumers' capital expenditures for plant and equipment attributable to both the electric and gas utility businesses.

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