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Significant Accounting Policies (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
EnerBank [Member]    
Significant Accounting Policies [Line Items]    
Unearned income $ 82 $ 62
Minimum [Member] | EnerBank [Member]    
Significant Accounting Policies [Line Items]    
Same as cash, fee recognition period 3 months  
Authorized contractor, fee recognition period 1 year  
Maximum [Member] | Consumers Energy Company [Member]    
Significant Accounting Policies [Line Items]    
Financial incentive as percentage of energy optimization program spending 15.00%  
Energy optimization spending limit 2.00%  
Maximum [Member] | EnerBank [Member]    
Significant Accounting Policies [Line Items]    
Same as cash, fee recognition period 24 months  
Authorized contractor, fee recognition period 12 years