Income Taxes (Details)	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
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	(4.90%)	(5.30%)
Other, net	(1.30%)	(0.70%)
Effective tax rate	33.60%	33.90%
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	(4.20%)	(4.30%)
Other, net	(1.50%)	(0.70%)
Effective tax rate	34.10%	34.90%