Reportable Segments (Reconciliation of Revenue from Segments to Consolidated) (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Operating Revenue	$ 1,364	$ 1,340	$ 3,419	$ 3,307
Total Net Income Available to Common Stockholders	100	80	235	165
Consumers Energy Company [Member] | Electric Utility [Member]
Operating Revenue	949	975	1,846	1,813
Total Net Income Available to Common Stockholders	85	86	150	127
Electric Utility [Member]
Operating Revenue	949	975	1,846	1,813
Total Net Income Available to Common Stockholders	85	86	150	127
Consumers Energy Company [Member] | Gas Utility [Member]
Operating Revenue	354	301	1,445	1,353
Total Net Income Available to Common Stockholders	5	1	93	67
Gas Utility [Member]
Operating Revenue	354	301	1,445	1,353
Total Net Income Available to Common Stockholders	5	1	93	67
Enterprises [Member]
Operating Revenue	50	55	105	123
Total Net Income Available to Common Stockholders	29	33	32	42
Consumers Energy Company [Member] | Other [Member]
Total Net Income Available to Common Stockholders	1		1
Other [Member]
Operating Revenue	11	9	23	18
Total Net Income Available to Common Stockholders	(19)	(24)	(42)	(54)
Discontinued Operations [Member]
Total Net Income Available to Common Stockholders		(16)	2	(17)
Consumers Energy Company [Member]
Operating Revenue	1,303	1,276	3,291	3,166
Total Net Income Available to Common Stockholders	$ 91	$ 87	$ 244	$ 194