Income Taxes (Details)	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
U.S. federal income tax rate	35.00%	35.00%
State and local income taxes, net of federal effect	4.80%	5.00%
Accelerated flow-through of regulatory tax benefits	(4.90%)	(5.40%)
Other, net	(1.30%)	(0.60%)
Effective tax rate	33.60%	34.00%
Consumers Energy Company [Member]
U.S. federal income tax rate	35.00%	35.00%
State and local income taxes, net of federal effect	4.80%	4.90%
Accelerated flow-through of regulatory tax benefits	(4.30%)	(4.50%)
Other, net	(1.50%)	(0.60%)
Effective tax rate	34.00%	34.80%