Financial Instruments (Schedule of Cost of Carrying Amounts and Fair Value of Long-Term Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Securities held to maturity, Cost or Carrying Amount	$ 7		$ 5
Securities held to maturity - fair value	7		6
Securities available for sale, Cost or Carrying Amount	113		90
Securities available for sale, fair value	113		90
Total unsecured consumer installment loans, net of an allowance for loan losses	480	[1]	386	[1]
Notes receivable, Fair Value	504	[1]	407	[1]
Long-term debt, Cost or Carrying Amount	7,073	[2]	7,174	[2]
Long-term Debt, Fair Value	8,025	[2]	7,861	[2]
Notes receivable	49		70
Current portion of long-term debt	1,033		726
Portion of long-term debt supported by third-party credit enhancements	103		103
CMS Energy Corporation [Member]
Notes receivable	1		1
Consumers Energy Company [Member]
Securities available for sale, Cost or Carrying Amount	81		64
Securities available for sale, fair value	109		90
Long-term debt, Cost or Carrying Amount	4,326	[3]	4,525	[3]
Long-term Debt, Fair Value	4,882	[3]	4,891	[3]
Notes receivable	23		55
Current portion of long-term debt	339		37
Portion of long-term debt supported by third-party credit enhancements	103		103
EnerBank USA [Member]
Total unsecured consumer installment loans, net of an allowance for loan losses	480		386
Notes receivable	$ 19		$ 11

[1] Includes current portion of notes receivable of $19 million at December 31, 2011 and $11 million at December 31, 2010.

[2] Includes current portion of long-term debt of $1.0 billion at December 31, 2011 and $726 million at December 31, 2010.

[3] Includes current portion of long-term debt of $339 million at December 31, 2011 and $37 million at December 31, 2010.