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Leases (Narrative) (Details) - Consumers Energy Company [Member]
12 Months Ended
Dec. 31, 2015
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 11 years
Gas Transportation Pipeline into Karn [Member]  
Leases [Line Items]  
Capital Lease Term 15 years
Capital Lease Remaining Term 6 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 2 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 17 years