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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)
$ in Millions
Mar. 31, 2016
Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Other liabilities current $ 118 $ 142
Current portion of long-term debt 929 684
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]    
Securities held to maturity - Fair Value 13 11
Long-term payable, Fair Value [1] 14 14
Long-term debt, Fair Value [2] 9,099 9,084
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 13 11
Long-term payable, Fair Value [1] 15 14
Long-term debt, Fair Value [2] 9,841 9,599
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Other liabilities current 87 109
Current portion of long-term debt 448 198
Consumers Energy Company [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [3] 5,382 5,381
Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [3] 5,853 5,684
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes receivable 151 144
EnerBank [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [4] 1,175 1,161
EnerBank [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [4] $ 1,256 $ 1,228
Fair Value, Inputs, Level 1 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value
Long-term payable, Fair Value [1]
Long-term debt, Fair Value [2]
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 debt, Fair Value [3]
Fair Value, Inputs, Level 1 [Member] | EnerBank [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [4]
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 [2] 8,856 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 [3] 4,868 4,733
Fair Value, Inputs, Level 3 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term payable, Fair Value [1] 15 14
Long-term debt, Fair Value [2] 985 951
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 debt, Fair Value [3] 985 951
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 [4] $ 1,256 $ 1,228
[1] Includes current portion of long-term payable of $1 million at March 31, 2016 and December 31, 2015.
[2] Includes current portion of long-term debt of $929 million at March 31, 2016 and $684 million at December 31, 2015.
[3] Includes current portion of long-term debt of $448 million at March 31, 2016 and $198 million at December 31, 2015.
[4] Includes current portion of notes receivable of $151 million at March 31, 2016 and $144 million at December 31, 2015.