Reportable Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating Revenue		$ 1,953	$ 1,829
Net income available to common stockholders		241	199
Plant, property, and equipment, gross		22,878		$ 22,506
Total Assets		22,868		23,050
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,855	1,737
Net income available to common stockholders		242	211
Plant, property, and equipment, gross		22,692		22,318
Total Assets		20,949		21,099
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,078	1,036
Net income available to common stockholders		139	124
Plant, property, and equipment, gross	[1]	15,432		15,221
Total Assets	[1]	13,986		13,906
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		1,078	1,036
Net income available to common stockholders		139	124
Plant, property, and equipment, gross	[1]	15,432		15,221
Total Assets	[1]	13,986		13,907
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue		777	701
Net income available to common stockholders		103	87
Plant, property, and equipment, gross	[1]	7,244		7,080
Total Assets	[1]	6,941		7,139
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue		777	701
Net income available to common stockholders		103	87
Plant, property, and equipment, gross	[1]	7,244		7,080
Total Assets	[1]	6,941		7,139
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue		63	59
Net income available to common stockholders		15	12
Plant, property, and equipment, gross		165		167
Total Assets		348		342
Other reconciling items [Member]
Segment Reporting Information [Line Items]
Operating Revenue		35	33
Net income available to common stockholders		(16)	$ (24)
Plant, property, and equipment, gross		37		38
Total Assets		1,593		1,663
Other reconciling items [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Plant, property, and equipment, gross		16		17
Total Assets		$ 22		$ 53

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