Plant, Property, and Equipment (Schedule Of Depreciation And Amortization) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization	$ 6,510	$ 6,056
Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	6,441	5,994
Utility Plant Assets [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization	6,439	5,993
Utility Plant Assets [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	6,439	5,993
Non-Utility Plant Assets [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization	71	63
Non-Utility Plant Assets [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ 2	$ 1