Reportable Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Operating Revenue	$ 1,979		$ 1,743
Total Net Income Available to Common Stockholders	144		67
Total Plant, Property, and Equipment, Gross	15,732			15,592
Total Assets	17,269			17,131
Consumers Energy Company [Member]
Operating Revenue	1,919		1,675
Total Net Income Available to Common Stockholders	162		76
Total Plant, Property, and Equipment, Gross	15,596			15,456
Total Assets	16,272			16,275
Electric Utility [Member]
Operating Revenue	961		836
Total Net Income Available to Common Stockholders	66		21
Total Plant, Property, and Equipment, Gross	11,118			11,041
Total Assets	10,640	[1]		10,423	[1]
Electric Utility [Member] | Consumers Energy Company [Member]
Operating Revenue	961		836
Total Net Income Available to Common Stockholders	66		21
Total Plant, Property, and Equipment, Gross	11,118			11,041
Total Assets	10,640	[1]		10,423	[1]
Gas Utility [Member]
Operating Revenue	958		839
Total Net Income Available to Common Stockholders	96		55
Total Plant, Property, and Equipment, Gross	4,463			4,400
Total Assets	4,698	[1]		5,016	[1]
Gas Utility [Member] | Consumers Energy Company [Member]
Operating Revenue	958		839
Total Net Income Available to Common Stockholders	96		55
Total Plant, Property, and Equipment, Gross	4,463			4,400
Total Assets	4,698	[1]		5,016	[1]
Enterprises [Member]
Operating Revenue	44		54
Total Net Income Available to Common Stockholders	4		5
Total Plant, Property, and Equipment, Gross	113			113
Total Assets	181			181
Other [Member]
Operating Revenue	16		14
Total Net Income Available to Common Stockholders	(22)		(14)
Total Plant, Property, and Equipment, Gross	38			38
Total Assets	1,750			1,511
Other [Member] | Consumers Energy Company [Member]
Total Plant, Property, and Equipment, Gross	15			15
Total Assets	$ 934			$ 836

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