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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value $ 13 $ 11
Accounts receivable, current 12  
Notes and accrued interest receivable 180 128
Other liabilities current 199 142
Current portion of long-term debt 864 684
DIG Note Payable [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Other liabilities current 1 1
Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes payable, Fair Value [1] 17 14
Long-term receivable, fair Value [2] 22  
Securities held to maturity - Fair Value 13 11
Long-term debt, Fair Value [3] 9,504 9,084
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes payable, Fair Value [1] 17 14
Long-term receivable, fair Value [2] 22  
Securities held to maturity - Fair Value 13 11
Long-term debt, Fair Value [3] 9,953 9,599
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes and accrued interest receivable 29  
Other liabilities current 164 109
Current portion of long-term debt 375 198
Consumers Energy Company [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [2] 22  
Notes receivable, Fair Value [4] 45  
Long-term debt, Fair Value [5] 5,628 5,381
Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [2] 22  
Notes receivable, Fair Value [4] 45  
Long-term debt, Fair Value [5] 5,903 5,684
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes and accrued interest receivable 219 144
EnerBank [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [3],[6] 1,326 1,161
EnerBank [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [3],[6] 1,415 1,228
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 13 11
Long-term debt, Fair Value [3] 8,990 8,648
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 [5] 4,940 4,733
Fair Value, Inputs, Level 3 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes payable, Fair Value [1] 17 14
Long-term receivable, fair Value [2] 22  
Long-term debt, Fair Value [3] 963 951
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 receivable, fair Value [2] 22  
Notes receivable, Fair Value [4] 45  
Long-term debt, Fair Value [5] 963 951
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 [3],[6] $ 1,415 $ 1,228
[1] Includes current portion of long-term payables of $1 million at December 31, 2016 and 2015.
[2] Includes current accounts receivable of $12 million at December 31, 2016.
[3] Includes current portion of long-term debt of $864 million at December 31, 2016 and $684 million at December 31, 2015.
[4] Includes current portion of notes receivable of $29 million at December 31, 2016.
[5] Includes current portion of long-term debt of $375 million at December 31, 2016 and $198 million at December 31, 2015.
[6] Includes current portion of notes receivable of $219 million at December 31, 2016 and $144 million at December 31, 2015.