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Financings and Capitalization (Preferred Stock of Subsidiary) (Details) - USD ($)
$ / shares in Units, $ in Millions
Dec. 31, 2015
Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Par value of Preferred Stock $ 0.01  
Shares of Preferred Stock authorized 10,000,000  
Consumers Energy Company [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Preferred stock Value $ 37 $ 37
Preferred Stock $4.50 Series [Member] | Consumers Energy Company [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Par value of Preferred Stock $ 100 $ 100
Shares of Preferred Stock authorized 7,500,000 7,500,000
Optional Redemption Price $ 110.00 $ 110.00
Number of Shares 373,148 373,148
Preferred stock Value $ 37 $ 37