Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,575	$ 1,546	$ 4,882	$ 5,050
Net income (loss) available to common stockholders	218	207	597	513
Plant, property, and equipment, gross	27,036		27,036		$ 25,390
Total Assets	29,280		29,280		26,837
Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,450	1,429	4,524	4,706
Net income (loss) available to common stockholder	230	213	624	536
Plant, property, and equipment, gross	25,893		25,893		24,963
Total Assets	24,836		24,836		23,699
Operating Segments | Electric Utility
Segment Reporting Information [Line Items]
Operating Revenue	1,257	1,250	3,307	3,380
Net income (loss) available to common stockholders	226	223	463	418
Plant, property, and equipment, gross	16,668		16,668		16,158
Total Assets	15,556		15,556		14,911
Operating Segments | Electric Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,257	1,250	3,307	3,380
Net income (loss) available to common stockholder	226	223	463	418
Plant, property, and equipment, gross	16,668		16,668		16,158
Total Assets	15,621		15,621		14,973
Operating Segments | Gas Utility
Segment Reporting Information [Line Items]
Operating Revenue	193	179	1,217	1,326
Net income (loss) available to common stockholders	4	(10)	162	119
Plant, property, and equipment, gross	9,204		9,204		8,785
Total Assets	9,148		9,148		8,659
Operating Segments | Gas Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	193	179	1,217	1,326
Net income (loss) available to common stockholder	4	(10)	162	119
Plant, property, and equipment, gross	9,204		9,204		8,785
Total Assets	9,196		9,196		8,706
Operating Segments | Enterprises
Segment Reporting Information [Line Items]
Operating Revenue	57	59	167	184
Net income (loss) available to common stockholders	13	7	34	30
Plant, property, and equipment, gross	1,109		1,109		405
Total Assets	1,250		1,250		527
Operating Segments | EnerBank
Segment Reporting Information [Line Items]
Operating Revenue	68	58	191	160
Net income (loss) available to common stockholders	12	11	34	32
Plant, property, and equipment, gross	34		34		22
Total Assets	3,125		3,125		2,692
Other reconciling items
Segment Reporting Information [Line Items]
Net income (loss) available to common stockholders	(37)	(24)	(96)	(86)
Plant, property, and equipment, gross	21		21		20
Total Assets	201		201		48
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Net income (loss) available to common stockholder	0	$ 0	(1)	$ (1)
Plant, property, and equipment, gross	21		21		20
Total Assets	$ 19		$ 19		$ 20