Financial Instruments (Schedule Of Cost/Carrying Amounts And Fair Values Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity, Cost or Carrying Amount	$ 8		$ 7
Securities held to maturity - Fair Value	9		7
Long-term debt, Cost or Carrying Amount	7,199	[1]	7,073	[1]
Long-term debt, Fair Value	8,251	[1]	8,025	[1]
Notes receivable	28		49
Current portion of long-term debt	488		1,033
Consumers Energy Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, Cost or Carrying Amount	4,348	[2]	4,326	[2]
Long-term debt, Fair Value	4,987	[2]	4,882	[2]
Notes receivable			23
Current portion of long-term debt	40		339
EnerBank USA [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable, Carrying Amount	513	[3]	480	[3]
Notes receivable, Fair Value	541	[3]	504	[3]
Notes receivable	27		19
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	9
Long-term debt, Fair Value	8,251	[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	4,987	[2]
Fair Value, Inputs, Level 3 [Member] | EnerBank USA [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable, Fair Value	$ 541	[3]

[1] Includes current portion of long-term debt of $488 million at September 30, 2012 and $1,033 million at December 31, 2011.

[2] Includes current portion of long-term debt of $40 million at September 30, 2012 and $339 million at December 31, 2011.

[3] In Millions September 30, 2012December 31, 2011Carrying Fair ValueCarrying Amount Total Level 1 Level 2 Level 3 Amount Fair Value CMS Energy, including ConsumersSecurities held to maturity$ 8$ 9$ -$ 9$ -$ 7$ 7Notes receivable1 513 541 - - 541 480 504Long-term debt2 7,199 8,251 - 8,251 - 7,073 8,025ConsumersLong-term debt3$ 4,348$ 4,987$ -$ 4,987$ -$ 4,326$ 4,882Includes current portion of notes receivable of $27 million at September 30, 2012 and $19 million at December 31, 2011.