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Stock-Based Compensation (Schedule Of Restricted Stock Activity) (Details) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Granted 841,413    
Consumers Energy Company [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Granted 801,235    
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Granted 826,075    
Number of Shares, Vested (819,658)    
Number of Shares, Forfeited (245,504)    
Weighted-Average Grant Date Fair Value per Share, Granted $ 31.74 $ 36.84 $ 26.15
Weighted-Average Grant Date Fair Value per Share, Vested 24.37    
Weighted-Average Grant Date Fair Value per Share, Forfeited $ 35.18    
Restricted Stock [Member] | Consumers Energy Company [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Granted 786,328    
Number of Shares, Vested (782,505)    
Number of Shares, Forfeited (234,523)    
Weighted-Average Grant Date Fair Value per Share, Granted $ 31.77 $ 36.83 $ 26.18
Weighted-Average Grant Date Fair Value per Share, Vested 24.39    
Weighted-Average Grant Date Fair Value per Share, Forfeited $ 35.17    
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Granted 15,338    
Number of Shares, Vested (13,588)    
Number of Shares, Forfeited 0 0  
Weighted-Average Grant Date Fair Value per Share, Granted $ 39.12 $ 34.25  
Weighted-Average Grant Date Fair Value per Share, Vested $ 33.22    
Restricted Stock Units (RSUs) [Member] | Consumers Energy Company [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Granted 14,907    
Number of Shares, Vested (13,233)    
Number of Shares, Forfeited 0 0  
Weighted-Average Grant Date Fair Value per Share, Granted $ 39.12 $ 34.25  
Weighted-Average Grant Date Fair Value per Share, Vested $ 33.23    
Restricted Stock and Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, at beginning of period 1,624,934    
Number of Shares, at end of period 1,387,597 1,624,934  
Weighted-Average Grant Date Fair Value per Share, at beginning of period $ 29.08    
Weighted-Average Grant Date Fair Value per Share, at end of period $ 32.44 $ 29.08  
Restricted Stock and Restricted Stock Units [Member] | Consumers Energy Company [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, at beginning of period 1,557,657    
Number of Shares, at end of period 1,328,631 1,557,657  
Weighted-Average Grant Date Fair Value per Share, at beginning of period $ 29.06    
Weighted-Average Grant Date Fair Value per Share, at end of period $ 32.41 $ 29.06