Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)
$ in Millions
Sep. 30, 2016
Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Other liabilities current $ 159 $ 142
Current portion of long-term debt 984 684
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]    
Long-term receivable, fair Value [1] 23  
Notes receivable, Fair Value [2] 1,286 1,161
Securities held to maturity - Fair Value 13 11
Long-term debt, Fair Value [3] 9,706 9,084
Long-term payables, Fair Value [4] 22 14
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [1] 23  
Notes receivable, Fair Value [2] 1,374 1,228
Securities held to maturity - Fair Value 14 11
Long-term debt, Fair Value [3] 10,651 9,599
Long-term payables, Fair Value [4] 23 14
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Other liabilities current 127 109
Current portion of long-term debt 275 198
Consumers Energy Company [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value 23  
Notes receivable, Fair Value 45  
Long-term debt, Fair Value [5] 5,640 5,381
Long-term payables, Fair Value 6  
Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value 23  
Notes receivable, Fair Value 44  
Long-term debt, Fair Value [5] 6,232 5,684
Long-term payables, Fair Value 6  
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes receivable 187 144
Other Receivables [Member] | Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Accounts receivable, current 13  
Fair Value, Inputs, Level 1 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [1]
Notes receivable, Fair Value [2]
Securities held to maturity - Fair Value
Long-term debt, Fair Value [3]
Long-term payables, Fair Value [4]
Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value
Notes receivable, Fair Value
Long-term debt, Fair Value [5]
Long-term payables, Fair Value
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 14 11
Long-term debt, Fair Value [3] 9,628 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] 5,209 4,733
Fair Value, Inputs, Level 3 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [1] 23  
Notes receivable, Fair Value [2] 1,374 1,228
Long-term debt, Fair Value [3] 1,023 951
Long-term payables, Fair Value [4] 23 14
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 23  
Notes receivable, Fair Value 44  
Long-term debt, Fair Value [5] 1,023 $ 951
Long-term payables, Fair Value $ 6  
[1] Includes current accounts receivable of $13 million at September 30, 2016.
[2] Includes current portion of notes receivable of $187 million at September 30, 2016 and $144 million at December 31, 2015.
[3] Includes current portion of long-term debt of $984 million at September 30, 2016 and $684 million at December 31, 2015.
[4] Includes current portion of long-term payables of $1 million at September 30, 2016 and December 31, 2015.
[5] Includes current portion of long-term debt of $275 million at September 30, 2016 and $198 million at December 31, 2015.