Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,725	$ 1,507	$ 5,296	$ 4,691
Net income available to common stockholders	186	218	711	597
Plant, property, and equipment, gross	29,450		29,450		$ 27,870
Assets	30,513		30,513		29,666
Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,644	1,450	5,074	4,524
Net income available to common stockholders	186	230	711	624
Plant, property, and equipment, gross	28,331		28,331		26,757
Assets	26,189		26,189		25,399
Other reconciling items
Segment Reporting Information [Line Items]
Net income available to common stockholders	(7)	(25)	(27)	(62)
Plant, property, and equipment, gross	22		22		21
Assets	3,177		3,177		3,132
Other reconciling items | Consumers Energy Company
Segment Reporting Information [Line Items]
Net income available to common stockholders	0	0	(1)	(1)
Plant, property, and equipment, gross	22		22		21
Assets	18		18		29
Electric Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue	1,419	1,257	3,713	3,307
Net income available to common stockholders	195	226	504	463
Plant, property, and equipment, gross	17,992		17,992		17,155
Assets	16,092		16,092		15,829
Electric Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	1,419	1,257	3,713	3,307
Net income available to common stockholders	195	226	504	463
Plant, property, and equipment, gross	17,992		17,992		17,155
Assets	16,154		16,154		15,893
Gas Utility | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue	225	193	1,361	1,217
Net income available to common stockholders	(9)	4	208	162
Plant, property, and equipment, gross	10,317		10,317		9,581
Assets	9,969		9,969		9,429
Gas Utility | Operating Segments | Consumers Energy Company
Segment Reporting Information [Line Items]
Operating Revenue	225	193	1,361	1,217
Net income available to common stockholders	(9)	4	208	162
Plant, property, and equipment, gross	10,317		10,317		9,581
Assets	10,017		10,017		9,477
Enterprises | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenue	81	57	222	167
Net income available to common stockholders	7	$ 13	26	$ 34
Plant, property, and equipment, gross	1,119		1,119		1,113
Assets	$ 1,275		$ 1,275		$ 1,276