Leases (Schedule of Rent Expense) (Details) - Consumers Energy Company [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Leases [Line Items]
Contingent rental expense	[1]	$ 82	$ 85	$ 77
PPAs [Member]
Leases [Line Items]
Minimum operating lease expense		6	6	6
Non-PPAs [Member]
Leases [Line Items]
Minimum operating lease expense		$ 19	$ 19	$ 21

[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.