Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,492		$ 1,449	$ 3,445		$ 3,278
Net income (loss) available to common stockholders		139		92	380		291
Plant, property, and equipment, gross		23,258			23,258			$ 22,506
Total Assets		23,312			23,312			23,050
Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue		1,395		1,362	3,250		3,099
Net income available to common stockholder		151		103	393		314
Plant, property, and equipment, gross		23,059			23,059			22,318
Total Assets		21,283			21,283			21,099
Operating Segments | Electric Utility
Segment Reporting Information [Line Items]
Operating Revenue		1,089		1,077	2,167		2,113
Net income (loss) available to common stockholders		130		94	269		218
Plant, property, and equipment, gross	[1]	15,646			15,646			15,221
Total Assets	[1]	14,075			14,075			13,906
Operating Segments | Electric Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue		1,089		1,077	2,167		2,113
Net income available to common stockholder		130		94	269		218
Plant, property, and equipment, gross	[1]	15,646			15,646			15,221
Total Assets	[1]	14,075			14,075			13,907
Operating Segments | Gas Utility
Segment Reporting Information [Line Items]
Operating Revenue		306		285	1,083		986
Net income (loss) available to common stockholders		21		9	124		96
Plant, property, and equipment, gross	[1]	7,397			7,397			7,080
Total Assets	[1]	7,187			7,187			7,139
Operating Segments | Gas Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue		306		285	1,083		986
Net income available to common stockholder		21		9	124		96
Plant, property, and equipment, gross	[1]	7,397			7,397			7,080
Total Assets	[1]	7,187			7,187			7,139
Operating Segments | Enterprises
Segment Reporting Information [Line Items]
Operating Revenue		61	[2]	55	124	[2]	114
Net income (loss) available to common stockholders		14		7	29		19
Plant, property, and equipment, gross		175			175			167
Total Assets		321			321			342
Other reconciling items
Segment Reporting Information [Line Items]
Operating Revenue		36	[3]	32	71	[3]	65
Net income (loss) available to common stockholders		(26)		$ (18)	(42)		$ (42)
Plant, property, and equipment, gross		40			40			38
Total Assets		1,729			1,729			1,663
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue		0			0
Plant, property, and equipment, gross		16			16			17
Total Assets		$ 21			$ 21			$ 53

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

[2] Amounts represent the enterprises segment’s operating revenue from independent power production and CMS ERM’s sales of energy commodities in support of the independent power production portfolio.

[3] Amount represents EnerBank’s operating revenue from unsecured consumer installment loans for financing home improvements.