Income Taxes (Details)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
U.S. federal income tax rate	35.00%	35.00%
State and local income taxes, net of federal effect	4.90%	5.00%
Accelerated flow-through of regulatory tax benefits	(5.30%)
Other, net	(0.70%)	0.70%
Effective tax rate	33.90%	40.70%
Consumers Energy Company [Member]
U.S. federal income tax rate	35.00%	35.00%
State and local income taxes, net of federal effect	4.90%	4.80%
Accelerated flow-through of regulatory tax benefits	(4.30%)
Other, net	(0.70%)	(0.20%)
Effective tax rate	34.90%	39.60%