Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,546	$ 1,599	$ 5,050	$ 5,044
Net income (loss) available to common stockholders	207	169	513	549
Plant, property, and equipment, gross	24,645		24,645		$ 24,400
Total Assets	26,009		26,009		24,529
Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,429	1,502	4,706	4,752
Net income (loss) available to common stockholder	213	180	536	573
Plant, property, and equipment, gross	24,214		24,214		23,963
Total Assets	22,938		22,938		22,025
Operating Segments | Electric Utility
Segment Reporting Information [Line Items]
Operating Revenue	1,250	1,313	3,380	3,480
Net income (loss) available to common stockholders	223	199	418	468
Plant, property, and equipment, gross	15,812		15,812		16,027
Total Assets	14,495		14,495		14,079
Operating Segments | Electric Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,250	1,313	3,380	3,480
Net income (loss) available to common stockholder	223	199	418	468
Plant, property, and equipment, gross	15,812		15,812		16,027
Total Assets	14,557		14,557		14,143
Operating Segments | Gas Utility
Segment Reporting Information [Line Items]
Operating Revenue	179	189	1,326	1,272
Net income (loss) available to common stockholders	(10)	(19)	119	105
Plant, property, and equipment, gross	8,382		8,382		7,919
Total Assets	8,312		8,312		7,806
Operating Segments | Gas Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	179	189	1,326	1,272
Net income (loss) available to common stockholder	(10)	(19)	119	105
Plant, property, and equipment, gross	8,382		8,382		7,919
Total Assets	8,359		8,359		7,853
Operating Segments | Enterprises
Segment Reporting Information [Line Items]
Operating Revenue	59	57	184	181
Net income (loss) available to common stockholders	7	4	18	33
Plant, property, and equipment, gross	406		406		412
Total Assets	500		500		540
Operating Segments | Enterprises | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	0	0	0	0
Other reconciling items
Segment Reporting Information [Line Items]
Operating Revenue	58	40	160	111
Net income (loss) available to common stockholders	(13)	(15)	(42)	(57)
Plant, property, and equipment, gross	45		45		42
Total Assets	2,702		2,702		2,104
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	0	0	0	0
Net income (loss) available to common stockholder	0	$ 0	(1)	$ 0
Plant, property, and equipment, gross	20		20		17
Total Assets	$ 22		$ 22		$ 29