Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Benefits [Line Items]
Interest and penalties	$ 0.0	$ 0.0	$ 0.0
IRS audit, adjustments to income tax expense	0.0
Consumers Energy Company [Member]
Income Tax Benefits [Line Items]
Reduction of income tax expense	39.0	39.0
Interest and penalties	0.0	$ 0.0	$ 0.0
IRS audit, adjustments to income tax expense	0.0
Electric Utility [Member] | Consumers Energy Company [Member]
Income Tax Benefits [Line Items]
Income tax benefits, to be returned to customers	$ 209.0
Tax benefit, distribution to customers, term	5 years
Gas Utility [Member] | Consumers Energy Company [Member]
Income Tax Benefits [Line Items]
Income tax benefits, to be returned to customers	$ 260.0
Tax benefit, distribution to customers, term	12 years