Plant, Property, and Equipment (Public Utilities Property Plant and Equipment Schedule of Accumulated Depreciation and Amortization) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization	$ 5,747	$ 5,415
Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	5,676	5,346
Utility Plant Assets [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization	5,674	5,345
Utility Plant Assets [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	5,674	5,345
Non-Utility Plant Assets [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated Depreciation, Depletion and Amortization	73	70
Non-Utility Plant Assets [Member] | Consumers Energy Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ 2	$ 1