Reportable Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,445		$ 1,507	$ 4,830		$ 4,583
Total Net Income Available to Common Stockholders	126		148	350		315
Total Plant, Property, and Equipment, Gross	16,566			16,566			15,592
Total Assets	16,986			16,986			17,131
Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,386		1,448	4,647		4,405
Total Net Income Available to Common Stockholders	152		162	413		359
Total Plant, Property, and Equipment, Gross	16,426			16,426			15,456
Total Assets	16,094			16,094			16,275
Electric Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,188		1,239	3,175		3,073
Total Net Income Available to Common Stockholders	156		165	315		297
Total Plant, Property, and Equipment, Gross	11,652			11,652			11,041
Total Assets	10,412	[1]		10,412	[1]		10,423	[1]
Electric Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,188		1,239	3,175		3,073
Total Net Income Available to Common Stockholders	156		165	315		297
Total Plant, Property, and Equipment, Gross	11,652			11,652			11,041
Total Assets	10,412	[1]		10,412	[1]		10,423	[1]
Gas Utility [Member]
Segment Reporting Information [Line Items]
Operating Revenue	198		209	1,472		1,332
Total Net Income Available to Common Stockholders	(4)		(3)	97		61
Total Plant, Property, and Equipment, Gross	4,759			4,759			4,400
Total Assets	5,039	[1]		5,039	[1]		5,016	[1]
Gas Utility [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Operating Revenue	198		209	1,472		1,332
Total Net Income Available to Common Stockholders	(4)		(3)	97		61
Total Plant, Property, and Equipment, Gross	4,759			4,759			4,400
Total Assets	5,039	[1]		5,039	[1]		5,016	[1]
Enterprises [Member]
Segment Reporting Information [Line Items]
Operating Revenue	44		44	136		136
Total Net Income Available to Common Stockholders	(4)		5	1		9
Total Plant, Property, and Equipment, Gross	116			116			113
Total Assets	188			188			181
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	15		15	47		42
Total Net Income Available to Common Stockholders	(22)		(19)	(63)		(52)
Total Plant, Property, and Equipment, Gross	39			39			38
Total Assets	1,347			1,347			1,511
Other [Member] | Consumers Energy Company [Member]
Segment Reporting Information [Line Items]
Total Net Income Available to Common Stockholders				1		1
Total Plant, Property, and Equipment, Gross	15			15			15
Total Assets	$ 643			$ 643			$ 836

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