Leases (Schedule of Rent Expense) (Details) (Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Leases [Line Items]
Contingent rental expense	$ 85	[1]	$ 77	[1]	$ 33	[1]
PPAs [Member]
Leases [Line Items]
Minimum operating lease expense	6		6		6
Non-PPAs [Member]
Leases [Line Items]
Minimum operating lease expense	$ 19		$ 21		$ 23

[1] Contingent rental expense is related to capital and operating lease PPAs and is based on delivery of energy and capacity in excess of minimum lease payments.