Reportable Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Operating Revenue	$ 1,406	$ 1,333	$ 3,385	$ 3,076
Total Net Income Available to Common Stockholders	80	100	224	167
Total Plant, Property, and Equipment, Gross	16,086		16,086		15,592
Total Assets	17,429		17,429		17,131
Consumers Energy Company [Member]
Operating Revenue	1,342	1,282	3,261	2,957
Total Net Income Available to Common Stockholders	99	121	261	197
Total Plant, Property, and Equipment, Gross	15,951		15,951		15,456
Total Assets	16,409		16,409		16,275
Electric Utility [Member]
Operating Revenue	1,026	998	1,987	1,834
Total Net Income Available to Common Stockholders	93	111	159	132
Total Plant, Property, and Equipment, Gross	11,275		11,275		11,041
Total Assets	10,769		10,769		10,423
Electric Utility [Member] | Consumers Energy Company [Member]
Operating Revenue	1,026	998	1,987	1,834
Total Net Income Available to Common Stockholders	93	111	159	132
Total Plant, Property, and Equipment, Gross	11,275		11,275		11,041
Total Assets	10,769		10,769		10,423
Gas Utility [Member]
Operating Revenue	316	284	1,274	1,123
Total Net Income Available to Common Stockholders	5	9	101	64
Total Plant, Property, and Equipment, Gross	4,661		4,661		4,400
Total Assets	4,922		4,922		5,016
Gas Utility [Member] | Consumers Energy Company [Member]
Operating Revenue	316	284	1,274	1,123
Total Net Income Available to Common Stockholders	5	9	101	64
Total Plant, Property, and Equipment, Gross	4,661		4,661		4,400
Total Assets	4,922		4,922		5,016
Enterprises [Member]
Operating Revenue	48	38	92	92
Total Net Income Available to Common Stockholders	1	(1)	5	4
Total Plant, Property, and Equipment, Gross	112		112		113
Total Assets	180		180		181
Other [Member]
Operating Revenue	16	13	32	27
Total Net Income Available to Common Stockholders	(19)	(19)	(41)	(33)
Total Plant, Property, and Equipment, Gross	38		38		38
Total Assets	1,558		1,558		1,511
Other [Member] | Consumers Energy Company [Member]
Total Net Income Available to Common Stockholders	1	1	1	1
Total Plant, Property, and Equipment, Gross	15		15		15
Total Assets	$ 718		$ 718		$ 836