Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Operating Revenue	$ 2,059	$ 1,953
Net income	213	241
Plant, property, and equipment, gross	24,729		$ 24,400
Total Assets	24,793		24,529
Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,943	1,855
Net income	226	242
Plant, property, and equipment, gross	24,300		23,963
Total Assets	22,052		22,025
Operating Segments | Electric Utility
Segment Reporting Information [Line Items]
Operating Revenue	1,103	1,078
Net income	105	139
Plant, property, and equipment, gross	16,196		16,027
Total Assets	14,237		14,079
Operating Segments | Electric Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,103	1,078
Net income	105	139
Plant, property, and equipment, gross	16,196		16,027
Total Assets	14,300		14,143
Operating Segments | Gas Utility
Segment Reporting Information [Line Items]
Operating Revenue	840	777
Net income	121	103
Plant, property, and equipment, gross	8,087		7,919
Total Assets	7,681		7,806
Operating Segments | Gas Utility | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	840	777
Net income	121	103
Plant, property, and equipment, gross	8,087		7,919
Total Assets	7,729		7,853
Operating Segments | Enterprises
Segment Reporting Information [Line Items]
Operating Revenue	67	63
Net income	1	15
Plant, property, and equipment, gross	404		412
Total Assets	524		540
Operating Segments | Enterprises | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	0	0
Other reconciling items
Segment Reporting Information [Line Items]
Operating Revenue	49	35
Net income	(14)	(16)
Plant, property, and equipment, gross	42		42
Total Assets	2,351		2,104
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	0	$ 0
Plant, property, and equipment, gross	17		17
Total Assets	$ 23		$ 29