Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,509	$ 1,486	$ 1,350	$ 2,111	$ 1,758	$ 1,430	$ 1,468	$ 2,523	$ 6,456	$ 7,179	$ 6,566
Depreciation and amortization										750	685	628
Income (loss) from equity method investees	[1]									14	15	13
Interest charges										396	407	398
Income tax expense (benefit)										271	250	302
Net Income Attributable to CMS Energy		106	148	67	202	96	94	83	204	523	477	452
Plant, property, and equipment, gross		18,943				17,721				18,943	17,721	16,184
Investments in equity method investees	[1]	64				61				64	61	59
Total Assets		20,340				19,185				20,340	19,185	17,290
Capital expenditures	[2]									1,741	1,616	1,408
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,439	1,417	1,281	2,028	1,672	1,359	1,387	2,382	6,165	6,800	6,321
Depreciation and amortization										744	678	622
Interest charges										250	250	245
Income tax expense (benefit)										302	306	346
Net Income Available to Common Stockholders		134	$ 160	$ 83	$ 215	117	$ 119	$ 108	$ 221	592	565	532
Plant, property, and equipment, gross		18,797				17,580				18,797	17,580	16,044
Total Assets		18,658				17,847				18,658	17,847	16,179
Capital expenditures	[2]									1,694	1,612	1,403
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue										4,249	4,436	4,173
Depreciation and amortization										567	522	484
Interest charges										178	181	179
Income tax expense (benefit)										224	211	242
Net Income Attributable to CMS Energy										437	384	363
Plant, property, and equipment, gross		13,059				12,230				13,059	12,230	11,186
Total Assets	[3]	12,676				11,582				12,676	11,582	10,487
Capital expenditures	[2]									1,136	1,139	996
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue										4,249	4,436	4,173
Depreciation and amortization										567	522	484
Interest charges										178	181	179
Income tax expense (benefit)										224	211	242
Net Income Available to Common Stockholders										437	384	363
Plant, property, and equipment, gross		13,059				12,230				13,059	12,230	11,186
Total Assets	[3]	12,676				11,582				12,676	11,582	10,487
Capital expenditures	[2]									1,136	1,139	996
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue										1,916	2,363	2,148
Depreciation and amortization										177	156	138
Interest charges										71	67	64
Income tax expense (benefit)										78	95	104
Net Income Attributable to CMS Energy										154	179	168
Plant, property, and equipment, gross		5,723				5,335				5,723	5,335	4,843
Total Assets	[3]	5,918				5,391				5,918	5,391	4,784
Capital expenditures	[2]									558	473	407
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue										1,916	2,363	2,148
Depreciation and amortization										177	156	138
Interest charges										71	67	64
Income tax expense (benefit)										78	95	104
Net Income Available to Common Stockholders										154	179	168
Plant, property, and equipment, gross		5,723				5,335				5,723	5,335	4,843
Total Assets	[3]	5,918				5,391				5,918	5,391	4,784
Capital expenditures	[2]									558	473	407
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue										190	299	181
Depreciation and amortization										4	4	3
Income (loss) from equity method investees	[1]									14	15	13
Income tax expense (benefit)										3	(1)	(4)
Net Income Attributable to CMS Energy										4	(1)	2
Plant, property, and equipment, gross		120				115				120	115	115
Investments in equity method investees	[1]	61				58				61	58	57
Total Assets		270				231				270	231	231
Capital expenditures	[2]									44	3	1
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue										101	81	64
Depreciation and amortization										2	3	3
Interest charges										147	159	155
Income tax expense (benefit)										(34)	(55)	(40)
Net Income Attributable to CMS Energy										(72)	(85)	(81)
Plant, property, and equipment, gross		41				41				41	41	40
Investments in equity method investees	[1]	3				3				3	3	2
Total Assets		1,476				1,981				1,476	1,981	1,788
Capital expenditures	[2]									3	1	4
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue											1
Interest charges										1	2	2
Net Income Available to Common Stockholders										1	2	1
Plant, property, and equipment, gross		15				15				15	15	15
Total Assets		$ 64				$ 874				$ 64	$ 874	$ 908

[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.