Leases (Narrative) (Details) (Consumers Energy Company [Member])	12 Months Ended
	Dec. 31, 2014
Leases [Line Items]
Finance Lease Term	15 years
Coal-Carrying Railcars [Member]
Leases [Line Items]
Operating leases without extension provisions, remaining term	10 years
Operating leases with extension provisions, remaining term	12 years
Gas Transportation Pipeline into Karn [Member]
Leases [Line Items]
Capital Lease Term	15 years
Capital Lease Remaining Term	7 years
Gas Transportation Pipeline into Zeeland [Member]
Leases [Line Items]
Capital Lease Term	5 years
Capital lease renewal term	5 years
Capital Lease Remaining Term	3 years
Minimum [Member] | Coal-Carrying Railcars [Member]
Leases [Line Items]
Operating leases, term	1 year
Minimum [Member] | Long-term PPAs [Member]
Leases [Line Items]
Lease term	1 year
Maximum [Member] | Coal-Carrying Railcars [Member]
Leases [Line Items]
Operating leases, term	15 years
Maximum [Member] | Vehicle Fleet Operations [Member]
Leases [Line Items]
Capital Lease Term	120 months
Maximum [Member] | Long-term PPAs [Member]
Leases [Line Items]
Lease term	18 years