Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity - Fair Value	$ 11		$ 10
Long-term debt, Fair Value	9,380	[1]	8,368	[1]
Current notes receivable	96		63
Current portion of long-term debt	669		541
Consumers Energy Company [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	5,691	[2]	4,940	[2]
Current notes receivable			14
Current portion of long-term debt	60		43
EnerBank [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivable, Fair Value	896	[3]	724	[3]
Current notes receivable	95		48
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity - Fair Value
Long-term debt, Fair Value		[1]		[1]
Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value		[2]		[2]
Fair Value, Inputs, Level 1 [Member] | EnerBank [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivable, Fair Value		[3]		[3]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity - Fair Value	11		10
Long-term debt, Fair Value	8,370	[1]	7,406	[1]
Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	4,681	[2]	3,978	[2]
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,010	[1]	962	[1]
Fair Value, Inputs, Level 3 [Member] | Consumers Energy Company [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,010	[2]	962	[2]
Fair Value, Inputs, Level 3 [Member] | EnerBank [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivable, Fair Value	896	[3]	724	[3]
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity - Fair Value	11		10
Long-term debt, Fair Value	8,711	[1]	7,642	[1]
Carrying Amount [Member] | Consumers Energy Company [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	5,290	[2]	4,622	[2]
Carrying Amount [Member] | EnerBank [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivable, Fair Value	$ 847	[3]	$ 683	[3]

[1] Includes current portion of long-term debt of $669 million at September 30, 2014 and $541 million at December 31, 2013.

[2] Includes current portion of long-term debt of $60 million at September 30, 2014 and $43 million at December 31, 2013.

[3] Includes current portion of notes receivable of $95 million at September 30, 2014 and $48 million at December 31, 2013.