Plant, Property, and Equipment (Public Utilities Property Plant and Equipment Schedule of Composite Depreciation Rate Table) (Details) (Consumers Energy Company [Member])	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Electric Utility Property [Member]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	3.20%	3.00%	3.00%
Gas Utility Property [Member]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.90%	2.90%	2.90%
Other property [Member]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	7.20%	7.40%	7.40%