Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, Carrying Amount	$ 10		$ 9
Securities held to maturity - Fair Value	10		10
Notes receivable, Carrying Amount	698		561
Long-term debt, Carrying Amount	7,642	[1]	7,229	[1]
Long-term debt, Fair Value	8,368	[1]	8,347	[1]
Current notes receivable	63		41
Current portion of long-term debt	541		519
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable, Carrying Amount	14		16
Long-term debt, Carrying Amount	4,622	[2]	4,338	[2]
Long-term debt, Fair Value	4,940	[2]	5,015	[2]
Current notes receivable	14
Current portion of long-term debt	43		41
EnerBank [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable, Carrying Amount	683	[3]	544	[3]
Notes receivable, Fair Value	724	[3]	581	[3]
Current notes receivable	48		40
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity - Fair Value	10		10
Long-term debt, Fair Value	7,406	[1]	7,321	[1]
Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, Fair Value	3,978	[2]	3,989	[2]
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, Fair Value	962	[1]	1,026	[1]
Fair Value, Inputs, Level 3 [Member] | Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, Fair Value	962	[2]	1,026	[2]
Fair Value, Inputs, Level 3 [Member] | EnerBank [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable, Fair Value	$ 724	[3]	$ 581	[3]

[1] Includes current portion of long-term debt of $541 million at December 31, 2013 and $519 million at December 31, 2012.

[2] Includes current portion of long-term debt of $43 million at December 31, 2013 and $41 million at December 31, 2012.

[3] Includes current portion of notes receivable of $48 million at December 31, 2013 and $40 million at December 31, 2012.