Related Party Transactions - Consumers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Purchased power - related parties	$ 83	$ 90	$ 90
Accounts payable - related parties, current	9	10
Accounts receivable - related parties	11	11
Consumers Energy Company [Member]
Related Party Transaction [Line Items]
Purchased power - related parties	83	89	$ 89
Accounts payable - related parties, current	15	12
Accounts receivable - related parties	17	1
Due to related parties	23	12
Investments	29	$ 38
Consumers Energy Company [Member] | Credit Agreement [Member]
Related Party Transaction [Line Items]
Maximum borrowing capacity	300
Amount outstanding	$ 0