Leases (Schedule of Rent Expense) (Details) (Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Operating Leases, Rent Expense, Contingent Rentals	$ 11	[1]	$ 14	[1]	$ 9	[1]
PPAs [Member]
Operating Leases, Rent Expense, Minimum Rentals	10		5		9
Non-PPAs [Member]
Operating Leases, Rent Expense, Minimum Rentals	$ 22		$ 22		$ 23

[1] Contingent rental expense comprises PPA energy and capacity payments and any other payments not associated with RECs. This expense is excluded from operating lease expense.