Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Income from continuing operations before income taxes	$ 604,000,000		$ 587,000,000.0		$ 324,000,000.0
Income from continuing operataions before income taxes	606,000,000		590,000,000		335,000,000
Income tax expense at statutory rate	211,000,000		205,000,000		114,000,000
MCIT law change, net of federal benefit	(32,000,000)	[1]
State and local income taxes, net of federal benefit	21,000,000		26,000,000		21,000,000
Income tax credit amortization	(4,000,000)		(4,000,000)		(4,000,000)
Medicare Part D exempt income	(6,000,000)	[2]	(6,000,000)	[2]	(6,000,000)	[2]
Plant basis differences	(1,000,000)		2,000,000		1,000,000
Tax credits, net	(1,000,000)		(3,000,000)		(9,000,000)
Valuation allowance	1,000,000		1,000,000		2,000,000
Other, net	2,000,000		3,000,000		(4,000,000)
Income Tax Expense	191,000,000		224,000,000		115,000,000
Effective income tax rate	31.60%		38.20%		35.50%
Deferred tax liabilities	(2,045,000,000)		(1,858,000,000)
Expense Reversal on Previous Benefit from the Medicare Subsidy			3,000,000
Consumers Energy Company [Member]
Income from continuing operataions before income taxes	734,000,000		688,000,000		456,000,000
Income tax expense at statutory rate	257,000,000		241,000,000		160,000,000
State and local income taxes, net of federal benefit	24,000,000		26,000,000		19,000,000
Income tax credit amortization	(4,000,000)		(4,000,000)		(4,000,000)
Medicare Part D exempt income	(6,000,000)		(9,000,000)		(6,000,000)
Plant basis differences	(1,000,000)		2,000,000		1,000,000
Tax credits, net	(1,000,000)		(3,000,000)		(7,000,000)
Other, net	(2,000,000)		1,000,000
Income Tax Expense	267,000,000		254,000,000		163,000,000
Effective income tax rate	36.40%		36.90%		35.70%
Recognition of regulatory asset related to law change	2,467,000,000		2,112,000,000
Deferred tax liabilities	(2,151,000,000)		(1,986,000,000)
Medicare Part D [Member] | Consumers Energy Company [Member]
Recognition of regulatory asset related to law change	98,000,000
State Jurisdiction [Member]
MCIT rate	6.00%
Deferred tax liabilities	32,000,000
State Jurisdiction [Member] | Consumers Energy Company [Member]
MCIT rate	6.00%
Reversal of net deferred tax assets related to MCIT law change	128,000,000
Recognition of regulatory asset related to law change	$ 128,000,000

[1] CMS Energy's effective tax rate for the year ended December 31, 2011 was reduced due to a one-time non-cash reduction in tax expense resulting from a change in Michigan tax law. In May 2011, Michigan enacted the MCIT, effective January 1, 2012. The MCIT, a simplified six percent corporate income tax, will replace the MBT, which is a complex multi-part business tax. Both the MBT and the MCIT are income taxes for financial reporting purposes, for which deferred income tax assets and liabilities are recorded. CMS Energy and Consumers remeasured their Michigan deferred income tax assets and liabilities at June 30, 2011 to reflect this change in law. Unlike the MBT, the MCIT does not allow future tax deductions to offset the book-tax differences that existed upon enactment of the tax. Due primarily to the elimination of these future tax deductions, Consumers has eliminated $128 million of net deferred tax assets associated with its utility book-tax temporary differences, recognizing a $128 million regulatory asset (not including the effects of income tax gross-ups), and in addition to the amounts related to Consumers, CMS Energy eliminated $32 million of net deferred tax liabilities associated with its non-utility book-tax temporary differences, recognizing a $32 million deferred income tax benefit.

[2] For the year ended December 31, 2010, CMS Energy recognized deferred tax expense of $3 million to reflect the enactment of the Health Care Acts. The law change prospectively repealed the tax deduction for the portion of the health care costs reimbursed by the Medicare Part D subsidy for taxable years beginning after December 31, 2012. Consumers has recorded a regulatory asset of $98 million at December 31, 2011 to reflect the expected recovery of additional future income taxes.