Reportable Segments (Reconciliation of Revenue from Segments to Consolidated) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Operating Revenue	$ 1,464	$ 1,443	$ 4,883	$ 4,750
Total Net Income Available to Common Stockholders	139	134	374	299
Consumers Energy Company [Member] | Electric Utility [Member]
Operating Revenue	1,180	1,154	3,026	2,967
Total Net Income Available to Common Stockholders	159	156	309	283
Electric Utility [Member]
Operating Revenue	1,180	1,154	3,026	2,967
Total Net Income Available to Common Stockholders	159	156	309	283
Consumers Energy Company [Member] | Gas Utility [Member]
Operating Revenue	217	216	1,662	1,569
Total Net Income Available to Common Stockholders	(5)	2	88	69
Gas Utility [Member]
Operating Revenue	217	216	1,662	1,569
Total Net Income Available to Common Stockholders	(5)	2	88	69
Enterprises [Member]
Operating Revenue	56	63	161	186
Total Net Income Available to Common Stockholders	4	9	36	51
Consumers Energy Company [Member] | Other [Member]
Total Net Income Available to Common Stockholders		1	1	1
Other [Member]
Operating Revenue	11	10	34	28
Total Net Income Available to Common Stockholders	(19)	(33)	(61)	(87)
Discontinued Operations [Member]
Total Net Income Available to Common Stockholders			2	(17)
Consumers Energy Company [Member]
Operating Revenue	1,397	1,370	4,688	4,536
Total Net Income Available to Common Stockholders	$ 154	$ 159	$ 398	$ 353