Leases (Narrative) (Details) (Consumers Energy Company [Member])	12 Months Ended
	Dec. 31, 2011 years
Gas Transportation Pipeline into Karn [Member]
Capital Lease Term	15
Capital Lease Remaining Term	10
Gas Transportation Pipeline into Zeeland [Member]
Capital Lease Term	12
Capital Lease Remaining Term	1
Coal-Carrying Railcars [Member]
Operating Leases Without Extension Provisions Expiration Time Period Remaining	12
Operating Leases With Extension Provisions Expiration Time Period Remaining	15
Vehicle Fleet Operations [Member]
Capital Lease Term	120
Minimum [Member] | Long-term PPAs [Member]
Capital Lease Term	1
Maximum [Member] | Long-term PPAs [Member]
Capital Lease Term	20