New Accounting Standards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unamortized debt issuance costs	$ 41
Current deferred tax liabilities		$ 66
Unrealized gain (loss) on investments, net of tax	3	1	$ 2
Consumers Energy Company [Member]
Unamortized debt issuance costs	23
Current deferred tax liabilities		80
Unrealized gain (loss) on investments, net of tax	$ 1	$ (4)	$ (1)