Derivative Instruments (Tables)
9 Months Ended
Sep. 30, 2011
Schedule of Fair Value of Derivative Instruments
In Millions  
            Derivative Assets             Derivative Liabilities  
            Fair Value at             Fair Value at  
    Balance                     Balance              
    Sheet     September 30,     December 31,     Sheet     September 30,     December 31,  
    Location     2011     2010     Location     2011     2010  
 
CMS Energy, including Consumers                                        
Derivatives not designated as hedging instruments                                        
Commodity contracts1
   Other assets   $ 2     $ 1     Other liabilities2   $ 3     $ 4  
 
Consumers
                                                
Derivatives not designated as hedging instruments                                        
Commodity contracts
   Other assets   $ 2     $ 1     Other liabilities   $ —     $ —  
 
1   Assets and liabilities are presented gross and exclude the impact of offsetting derivative assets and liabilities under master netting agreements, which was less than $1 million at September 30, 2011 and December 31, 2010.
 
2   Liabilities exclude the impact of offsetting cash margin deposits paid by CMS ERM to other parties, which was less than $1 million at September 30, 2011 and December 31, 2010. CMS Energy presents these liabilities net of these impacts on its consolidated balance sheets.
Gain/(Loss) Recognized in Income for Derivative Instruments
                                 
In Millions
    Amount of Gain (Loss) on Derivatives Recognized in Income
    Three Months Ended
September 30		     Nine Months Ended
September 30
Location of Gain (Loss) on
Derivatives Recognized in Income		   2011     2010     2011     2010  
 
CMS Energy
                                
Commodity contracts
                                
Operating revenue
   $ (1 )   $ 2     $ (1 )   $ 5  
Fuel for electric generation
     —       1       —       3  
Purchased and interchange power
     —       1       —       2  
 
Total CMS Energy
   $ (1 )   $ 4     $ (1 )   $ 10  
 
Consumers Energy Company [Member]
 
Schedule of Fair Value of Derivative Instruments
In Millions
    Derivative Assets     Derivative Liabilities
    Balance     Fair Value at     Balance     Fair Value at
    Sheet     September 30,     December 31,     Sheet     September 30,     December 31,  
    Location     2011     2010     Location     2011     2010  
 
CMS Energy, including Consumers                                
Derivatives not designated as hedging instruments                                
Commodity contracts1
   Other assets   $ 2     $ 1     Other liabilities2   $ 3     $ 4  
 
Consumers
                                                
Derivatives not designated as hedging instruments                                
Commodity contracts
   Other assets   $ 2     $ 1     Other liabilities   $ —     $ —  
 
1     Assets and liabilities are presented gross and exclude the impact of offsetting derivative assets and liabilities under master netting agreements, which was less than $1 million at September 30, 2011 and December 31, 2010.
2     Liabilities exclude the impact of offsetting cash margin deposits paid by CMS ERM to other parties, which was less than $1 million at September 30, 2011 and December 31, 2010. CMS Energy presents these liabilities net of these impacts on its consolidated balance sheets.