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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)
$ in Millions
Sep. 30, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes receivable $ 119 $ 98
Current portion of long-term debt 720 519
Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 12 11
Long-term debt, Fair Value [1] 8,623 8,535
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 12 11
Long-term debt, Fair Value [1] 9,229 9,285
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current portion of long-term debt 261 124
Consumers Energy Company [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [2] 5,230 5,278
Consumers Energy Company [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [2] 5,613 5,749
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current notes receivable 136 138
EnerBank [Member] | Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [3] 1,077 938
EnerBank [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value [3] $ 1,150 $ 995
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 debt, Fair Value [1]
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 [2]
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 [3]
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 $ 12 $ 11
Long-term debt, Fair Value [1] 8,211 8,252
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 [2] 4,595 4,716
Fair Value, Inputs, Level 3 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value [1] 1,018 1,033
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 [2] 1,018 1,033
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] $ 1,150 $ 995
[1] Includes current portion of long-term debt of $720 million at September 30, 2015 and $519 million at December 31, 2014.
[2] Includes current portion of long-term debt of $261 million at September 30, 2015 and $124 million at December 31, 2014.
[3] Includes current portion of notes receivable of $136 million at September 30, 2015 and $138 million at December 31, 2014.