Reportable Segments (Reconciliation of Assets from Segment to Consolidated) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Plant, property, and equipment, gross	$ 14,607		$ 14,145
Total Assets	15,958		15,616
Consumers Energy Company [Member] | Electric Utility [Member]
Plant, property, and equipment, gross	10,311	[1]	9,944	[1]
Total Assets	9,607	[1]	9,321	[1]
Electric Utility [Member]
Plant, property, and equipment, gross	10,311	[1]	9,944	[1]
Total Assets	9,607	[1]	9,321	[1]
Consumers Energy Company [Member] | Gas Utility [Member]
Plant, property, and equipment, gross	4,149	[1]	4,063	[1]
Total Assets	4,852	[1]	4,614	[1]
Gas Utility [Member]
Plant, property, and equipment, gross	4,149	[1]	4,063	[1]
Total Assets	4,852	[1]	4,614	[1]
Enterprises [Member]
Plant, property, and equipment, gross	109		102
Total Assets	170		191
Consumers Energy Company [Member] | Other [Member]
Plant, property, and equipment, gross	15		15
Total Assets	599		904
Other [Member]
Plant, property, and equipment, gross	38		36
Total Assets	1,329		1,490
Consumers Energy Company [Member]
Plant, property, and equipment, gross	14,475		14,022
Total Assets	$ 15,058		$ 14,839

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