Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
U.S. federal income tax rate			35.00%	35.00%
MCIT law change, net of federal benefit				(9.90%)
State and local income taxes, net of federal benefit			4.70%	3.50%
Other, net			(0.20%)	(1.40%)
Effective income tax rate			39.50%	27.20%
Net income	$ (101)	$ (101)	$ (168)	$ (236)
Consumers Energy Company [Member]
U.S. federal income tax rate			35.00%	35.00%
State and local income taxes, net of federal benefit			5.30%	3.40%
Other, net			(0.30%)	(1.40%)
Effective income tax rate			40.00%	37.00%
Net income	(122)	(92)	(198)	(245)
Internal Revenue Service (IRS) [Member]
Net operating loss carryforward	45		45
Net income			$ 1