Leases (Schedule of Rent Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Operating Leases, Rent Expense, Contingent Rentals	$ 33		$ 11		$ 14
Consumers Energy Company [Member]
Operating Leases, Rent Expense, Contingent Rentals	33	[1]	11	[1]	14	[1]
PPAs [Member]
Operating Leases, Rent Expense, Minimum Rentals	6		10		5
PPAs [Member] | Consumers Energy Company [Member]
Operating Leases, Rent Expense, Minimum Rentals	6		10		5
Non-PPAs [Member]
Operating Leases, Rent Expense, Minimum Rentals	23		22		22
Non-PPAs [Member] | Consumers Energy Company [Member]
Operating Leases, Rent Expense, Minimum Rentals	$ 23		$ 22		$ 22

[1] Contingent rental expense is related to capital and operating lease PPAs.