Financial Instruments (Schedule of Cost of Carrying Amounts and Fair Value of Long-Term Financial Instruments) (Details) (USD $) In Millions	Jun. 30, 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	115		90
Securities available for sale, fair value	116		90
Total unsecured consumer installment loans, net of an allowance for loan losses	398	[1]	386	[1]
Notes receivable, Fair Value	417	[1]	407	[1]
Long-term debt, Cost or Carrying Amount	7,283	[2]	7,174	[2]
Long-term Debt, Fair Value	8,074	[2]	7,861	[2]
EnerBank's Loans classified as current Notes receivable	57		70
Current portion of long-term debt	1,099		726
Portion of long-term debt supported by third-party credit enhancements	103		103
Consumers Energy Company [Member]
Securities available for sale, Cost or Carrying Amount	82		64
Securities available for sale, fair value	107		90
Long-term debt, Cost or Carrying Amount	4,507	[3]	4,525	[3]
Long-term Debt, Fair Value	4,892	[3]	4,891	[3]
EnerBank's Loans classified as current Notes receivable	43		55
Current portion of long-term debt	338		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	398		386
EnerBank's Loans classified as current Notes receivable	13		11
Notes receivable	$ 13		$ 11

[1] Includes current portion of notes receivable of $13 million at June 30, 2011 and $11 million at December 31, 2010.

[2] Includes current portion of long-term debt of $1,099 million at June 30, 2011 and $726 million at December 31, 2010.

[3] Includes current portion of long-term debt of $338 million at June 30, 2011 and $37 million at December 31, 2010.