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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value $ 16 $ 13
Accounts receivable, current 14 12
Notes and accrued interest receivable 198 180
Notes receivable and held for sale 200 219
Other liabilities current 195 199
Current portion of long-term debt 1,081 864
DIG Note Payable [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Other liabilities current 3 1
Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes payable, Fair Value [1] 27 17
Long-term receivable, fair Value [2] 21 22
Notes receivable, Fair Value [3],[4] 1,371 1,326
Securities held to maturity - Fair Value 16 13
Long-term debt, Fair Value [3] 10,204 9,504
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes payable, Fair Value [1] 26 17
Long-term receivable, fair Value [2] 21 22
Notes receivable, Fair Value [3],[4] 1,464 1,415
Securities held to maturity - Fair Value 16 13
Long-term debt, Fair Value [3] 10,715 9,953
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes and accrued interest receivable 17 29
Other liabilities current 159 164
Current portion of long-term debt 343 375
Consumers Energy Company [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [2] 21 22
Notes receivable, Fair Value [5] 17 45
Long-term debt, Fair Value [6] 5,904 5,628
Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term receivable, fair Value [2] 21 22
Notes receivable, Fair Value [5] 17 45
Long-term debt, Fair Value [6] 6,236 5,903
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 16 13
Long-term debt, Fair Value [3] 9,363 8,990
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] 4,883 4,940
Fair Value, Inputs, Level 3 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes payable, Fair Value [1] 26 17
Long-term receivable, fair Value [2] 21 22
Notes receivable, Fair Value [3],[4] 1,464 1,415
Long-term debt, Fair Value [3] 1,352 963
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] 21 22
Notes receivable, Fair Value [5] 17 45
Long-term debt, Fair Value [6] $ 1,353 $ 963
[1] Includes current portion of long-term payables of $3 million at December 31, 2017 and $1 million at December 31, 2016.
[2] Includes current accounts receivable of $14 million at December 31, 2017 and $12 million at December 31, 2016.
[3] Includes current portion of long-term debt of $1.1 billion at December 31, 2017 and $864 million at December 31, 2016.
[4] Includes current portion of notes receivable of $200 million at December 31, 2017 and $219 million at December 31, 2016.
[5] Includes current portion of notes receivable of $17 million at December 31, 2017 and $29 million at December 31, 2016.
[6] Includes current portion of long-term debt of $343 million at December 31, 2017 and $375 million at December 31, 2016.