Reportable Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenue	$ 2,111		$ 2,523
Total net income available to common stockholders	202		204
Plant, property, and equipment, gross	17,930			17,721
Total Assets	19,198			19,185
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue	2,028		2,382
Total net income available to common stockholders	215		221
Plant, property, and equipment, gross	17,788			17,580
Total Assets	17,854			17,847
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,033		1,224
Total net income available to common stockholders	94		100
Plant, property, and equipment, gross	12,397	[1]		12,230	[1]
Total Assets	11,851	[1]		11,582	[1]
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,033		1,224
Total net income available to common stockholders	94		100
Plant, property, and equipment, gross	12,397	[1]		12,230	[1]
Total Assets	11,851	[1]		11,582	[1]
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue	995		1,158
Total net income available to common stockholders	121		121
Plant, property, and equipment, gross	5,376	[1]		5,335	[1]
Total Assets	5,092	[1]		5,391	[1]
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue	995		1,158
Total net income available to common stockholders	121		121
Plant, property, and equipment, gross	5,376	[1]		5,335	[1]
Total Assets	5,092	[1]		5,391	[1]
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue	60		122
Total net income available to common stockholders	7		2
Plant, property, and equipment, gross	118			115
Total Assets	234			231
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	23		19
Total net income available to common stockholders	(20)		(19)
Plant, property, and equipment, gross	39			41
Total Assets	2,021			1,981
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Plant, property, and equipment, gross	15			15
Total Assets	$ 911			$ 874

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