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Plant, Property, and Equipment (Property, Plant and Equipment Table) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Construction work in progress $ 1,080 $ 783  
Accumulated Depreciation and Amortization (5,121) (4,901)  
Public Utilities, Property, Plant and Equipment, Net 11,551 [1] 10,633 [1]  
Public Utilities, Property Plant and Equipment Additions 999 700  
Public Utilities, Property Plant and Equipment Disposals 168 104  
Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 8 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 51 years    
Capital Leased Assets, Gross 285 280 278
Other non-utility property 15 15  
Construction work in progress 1,080 782  
Accumulated Depreciation and Amortization (5,061) (4,846)  
Public Utilities, Property, Plant and Equipment, Net 11,475 [1] 10,557 [1]  
Public Utilities, Property Plant and Equipment Additions 999 700  
Public Utilities, Property Plant and Equipment Disposals 168 104  
Electricity Generation Plant, Non-Nuclear [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 22 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 125 years    
Public Utilities, Property, Plant and Equipment, Generation or Processing 4,254 3,936  
Electricity Generation Plant, Non-Nuclear [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 22 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 125 years    
Public Utilities, Property, Plant and Equipment, Generation or Processing 4,254 3,936  
Electric Distribution [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 23 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 75 years    
Public Utilities, Property, Plant and Equipment, Distribution 5,831 5,538  
Electric Distribution [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 23 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 75 years    
Public Utilities, Property, Plant and Equipment, Distribution 5,831 5,538  
Electric Other [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 5 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 50 years    
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment 677 651  
Electric Other [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 5 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 50 years    
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment 677 651  
Electric Capital Leases [Member]
      
Capital Leased Assets, Gross 279 275  
Electric Capital Leases [Member] | Consumers Energy Company [Member]
      
Capital Leased Assets, Gross 279 275  
Gas Distribution [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 30 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 80 years    
Public Utilities, Property, Plant and Equipment, Distribution 2,861 2,754  
Gas Distribution [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 30 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 80 years    
Public Utilities, Property, Plant and Equipment, Distribution 2,861 2,754  
Gas Transmission [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 13 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 75 years    
Public Utilities, Property, Plant and Equipment, Transmission 770 722  
Gas Transmission [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 13 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 75 years    
Public Utilities, Property, Plant and Equipment, Transmission 770 722  
Gas Underground Storage Facilities [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 30 years [2]    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 65 years [2]    
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment 339 [2] 322 [2]  
Gas Underground Storage Facilities [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 30 years [2]    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 65 years [2]    
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment 339 [2] 322 [2]  
Gas Other [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 5 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 50 years    
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment 424 403  
Gas Other [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 5 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 50 years    
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment 424 403  
Gas Capital Leases [Member]
      
Capital Leased Assets, Gross 6 5  
Gas Capital Leases [Member] | Consumers Energy Company [Member]
      
Capital Leased Assets, Gross 6 5  
Enterprises IPP [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 3 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 30 years    
Plant, property, and equipment, gross 89 89  
Enterprises Other [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 3 years    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 40 years    
Plant, property, and equipment, gross 24 20  
Other [Member]
      
Public Utilities, Property, Plant and Equipment, Useful Life, Minimum 1 year    
Public Utilities, Property, Plant and Equipment, Useful Life, Maximum 51 years    
Other non-utility property 38 36  
Base Natural Gas [Member] | Gas Underground Storage Facilities [Member]
      
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment 26 26  
Base Natural Gas [Member] | Gas Underground Storage Facilities [Member] | Consumers Energy Company [Member]
      
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment $ 26 $ 26  
[1] For the year ended December 31, 2012, utility plant additions were $999 million and utility plant retirements were $168 million. For the year ended December 31, 2011, utility plant additions were $700 million and utility plant retirements were $104 million.
[2] Underground storage includes base natural gas of $26 million at December 31, 2012 and 2011. Base natural gas is not subject to depreciation.