Plant, Property, and Equipment (Schedule of Finite Lived Intangible Assets Amortization Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Amortization of Intangible Assets	$ 39	$ 32	$ 28
Consumers Energy Company [Member]
Amortization of Intangible Assets	38	32	27
Software and Software Development Costs [Member]
Amortization of Intangible Assets	31	24	19
Software and Software Development Costs [Member] | Consumers Energy Company [Member]
Amortization of Intangible Assets	30	24	19
Minimum [Member]
Expected future amortization expense of intangible assets, per year	46
Minimum [Member] | Consumers Energy Company [Member]
Expected future amortization expense of intangible assets, per year	46
Maximum [Member]
Expected future amortization expense of intangible assets, per year	56
Maximum [Member] | Consumers Energy Company [Member]
Expected future amortization expense of intangible assets, per year	$ 56