Financings (Major Long-Term Debt Transactions) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Consumers Energy Company [Member] | Debt Issuances [Member] | April 2018 Tax-Exempt Bonds [Member]
Debt Issuance, Principal	$ 68	[1]
Debt Issuance Date	May 2011	[1]
Maturity Date	Apr. 15, 2018
Consumers Energy Company [Member] | Debt Issuances [Member] | April 2035 Tax Exempt Bonds [Member]
Debt Issuance, Principal	35	[1]
Debt Issuance Date	May 2011	[1]
Maturity Date	Apr. 01, 2035	[1]
Debt Issuances [Member]
Debt Issuance, Principal	353
Debt Issuances [Member] | Senior Notes [Member]
Debt Issuance, Principal	250
Interest Rate	2.75%
Debt Issuance Date	May 2011
Maturity Date	May 15, 2014
Consumers Energy Company [Member] | Debt Retirements [Member]
Debt Retirement, Principal	103
Consumers Energy Company [Member] | Debt Retirements [Member] | April 2018 Tax-Exempt Bonds [Member]
Maturity Date	Apr. 01, 2018	[1]
Debt Retirement, Principal	68	[1]
Debt Retirement Date	May 2011	[1]
Consumers Energy Company [Member] | Debt Retirements [Member] | April 2035 Tax Exempt Bonds [Member]
Maturity Date	Apr. 01, 2035	[1]
Debt Retirement, Principal	$ 35	[1]
Debt Retirement Date	May 2011	[1]
Consumers Energy Company [Member] | April 2018 Tax-Exempt Bonds [Member]
Interest Rate	0.26%
Consumers Energy Company [Member] | April 2035 Tax Exempt Bonds [Member]
Interest Rate	0.28%

[1] In May 2011, Consumers utilized the Michigan Strategic Fund for the issuance of $68 million and $35 million of tax-exempt Michigan Strategic Fund Variable Rate Limited Obligation Revenue Bonds. The initial interest rate, which resets weekly, was 0.26 percent for the $68 million bond issuance and 0.28 percent for the $35 million bond issuance. The bonds, which are backed by letters of credit and collateralized by FMBs, are subject to optional tender by the holders that would result in remarketing. Consumers used the proceeds to redeem $103 million of tax-exempt bonds in May 2011.