Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Unbilled receivables	$ 481	$ 361
Consumers Energy Company [Member]
Significant Accounting Policies [Line Items]
Unbilled receivables	$ 481	$ 361
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 waste reduction program spending	20.00%
Maximum [Member] | EnerBank [Member]
Significant Accounting Policies [Line Items]
Same as cash, fee recognition period	24 months
Authorized contractor, fee recognition period	12 years