Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
EnerBank [Member]
Significant Accounting Policies [Line Items]
Unearned income	$ 82	$ 62
Minimum [Member] | EnerBank [Member]
Significant Accounting Policies [Line Items]
Same as cash, fee recognition period	3 months
Authorized contractor, fee recognition period	1 year
Maximum [Member] | Consumers Energy Company [Member]
Significant Accounting Policies [Line Items]
Financial incentive as percentage of energy optimization program spending	15.00%
Energy optimization spending limit	2.00%
Maximum [Member] | EnerBank [Member]
Significant Accounting Policies [Line Items]
Same as cash, fee recognition period	24 months
Authorized contractor, fee recognition period	12 years