Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Jun. 30, 2011	Sep. 30, 2011	Sep. 30, 2010
U.S. federal income tax rate		35.00%	35.00%
MCIT law change, net of federal expense		(5.90%)
State and local income taxes, net of federal benefit		3.40%	4.00%
Medicare Part D exempt income, net of law change		(0.90%)	(0.90%)
Income tax credit amortization		(0.60%)	(0.60%)
Other, net		0.10%	0.90%
Effective income tax rate		31.10%	38.40%
MCIT rate	6.00%
Expense Reversal on Previous Benefit from the Medicare Subsidy			$ 3
Consumers Energy Company [Member] | Michigan Single Business Tax [Member]
Reversal of net deferred tax assets related to MCIT law change	134
Recognition of regulatory asset related to MCIT law change	134
Michigan Single Business Tax [Member]
Elimination of deferred tax liabilities related to MCIT law change	32
Recognition of tax benefit related to MCIT law change	32
Consumers Energy Company [Member]
U.S. federal income tax rate		35.00%	35.00%
State and local income taxes, net of federal benefit		3.10%	3.50%
Medicare Part D exempt income, net of law change		(0.80%)	(1.30%)
Plant basis differences		0.20%	0.30%
Income tax credit amortization		(0.50%)	(0.50%)
Other, net		(0.30%)	(0.20%)
Effective income tax rate		36.70%	36.80%
MCIT rate	6.00%