Plant, Property, and Equipment (Public Utilities Property Plant and Equipment Schedule of Composite Depreciation Rate Table) (Details) - Consumers Energy Company	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Electric utility property
Public Utility, Property, Plant and Equipment [Line Items]
Composite depreciation rate	3.90%	3.90%	3.90%
Gas utility property
Public Utility, Property, Plant and Equipment [Line Items]
Composite depreciation rate	2.90%	2.90%	2.90%
Other property
Public Utility, Property, Plant and Equipment [Line Items]
Composite depreciation rate	10.10%	10.00%	9.80%