Plant, Property, and Equipment (Public Utilities Property Plant and Equipment Schedule of Accumulated Depreciation and Amortization) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accumulated Depreciation, Depletion and Amortization	$ 5,121	$ 4,901
Consumers Energy Company [Member]
Accumulated Depreciation, Depletion and Amortization	5,061	4,846
Utility Plant Assets [Member]
Accumulated Depreciation, Depletion and Amortization	5,060	4,844
Utility Plant Assets [Member] | Consumers Energy Company [Member]
Accumulated Depreciation, Depletion and Amortization	5,060	4,844
Non-Utility Plant Assets [Member]
Accumulated Depreciation, Depletion and Amortization	61	57
Non-Utility Plant Assets [Member] | Consumers Energy Company [Member]
Accumulated Depreciation, Depletion and Amortization	$ 1	$ 2