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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes and accrued interest receivable $ 201 $ 198
Other liabilities current 134 195
Current portion of long-term debt 1,300 1,100
DIG Note Payable [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Other liabilities current 2 3
Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [1] 20 21
Notes receivable, Fair Value [2] 1,370 1,371
Securities held to maturity - Fair Value 17 16
Long-term debt, Fair Value [3] 10,261 10,204
Long-term payables, Fair Value [4] 25 27
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [1] 20 21
Notes receivable, Fair Value [2] 1,453 1,464
Securities held to maturity - Fair Value 17 16
Long-term debt, Fair Value [3] 10,273 10,715
Long-term payables, Fair Value [4] 26 26
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes and accrued interest receivable 17 17
Other liabilities current 103 159
Current portion of long-term debt 693 343
Consumers Energy Company [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [1] 20 21
Notes receivable, Fair Value [5] 17 17
Long-term debt, Fair Value [6] 5,904 5,904
Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [1] 20 21
Notes receivable, Fair Value [5] 17 17
Long-term debt, Fair Value [6] 6,034 6,236
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes receivable 203 200
Other Receivables [Member] | Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Accounts receivable, current 13 14
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 [1]
Notes receivable, Fair Value [5]
Long-term debt, Fair Value [6]
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 17 16
Long-term debt, Fair Value [3] 8,971 9,363
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 [6] 4,732 4,883
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] 20 21
Notes receivable, Fair Value [2] 1,453 1,464
Long-term debt, Fair Value [3] 1,302 1,352
Long-term payables, Fair Value [4] 26 26
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 [1] 20 21
Notes receivable, Fair Value [5] 17 17
Long-term debt, Fair Value [6] $ 1,302 $ 1,353
[1] Includes current accounts receivable of $13 million at March 31, 2018 and $14 million at December 31, 2017.
[2] Includes current portion of notes receivable of $203 million at March 31, 2018 and $200 million at December 31, 2017.
[3] Includes current portion of long-term debt of $1.3 billion at March 31, 2018 and $ 1.1 billion at December 31, 2017.
[4] Includes current portion of long-term payables of $2 million at March 31, 2018 and $3 million at December 31, 2017.
[5] Includes current portion of notes receivable of $17 million at March 31, 2018 and $17 million at December 31, 2017.
[6] Includes current portion of long-term debt of $693 million at March 31, 2018 and $343 million at December 31, 2017.