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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)
$ in Millions
Dec. 31, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value $ 11 $ 11
Current notes payable 249 60
Current notes receivable 128 98
Current portion of long-term debt 684 519
DIG Note Payable [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes payable 1  
Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 11 11
Notes payable, Fair Value [1],[2] 14  
Long-term debt, Fair Value [3] 9,125 8,535
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 11 11
Notes payable, Fair Value [1],[2] 14  
Long-term debt, Fair Value [3] 9,599 9,285
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes payable 249 60
Current portion of long-term debt 198 124
Consumers Energy Company [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [4] 5,404 5,278
Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [4] 5,684 5,749
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes receivable 144 138
EnerBank [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [2],[3] 1,161 938
EnerBank [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [2],[3] 1,228 995
Fair Value, Inputs, Level 2 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 11 11
Long-term debt, Fair Value [3] 8,648 8,252
Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [4] 4,733 4,716
Fair Value, Inputs, Level 3 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes payable, Fair Value [1],[2] 14  
Long-term debt, Fair Value [3] 951 1,033
Fair Value, Inputs, Level 3 [Member] | Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [4] 951 1,033
Fair Value, Inputs, Level 3 [Member] | EnerBank [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [2],[3] $ 1,228 $ 995
[1] Includes current portion of notes payable of $1 million at December 31, 2015.
[2] Includes current portion of notes receivable of $144 million at December 31, 2015 and $138 million at December 31, 2014.
[3] Includes current portion of long-term debt of $684 million at December 31, 2015 and $519 million at December 31, 2014.
[4] Includes current portion of long-term debt of $198 million at December 31, 2015 and $124 million at December 31, 2014.