Income Taxes (Narrative) (Details) - Consumers Energy Company [Member] - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Income Tax Benefits [Line Items]
Reduction of income tax expense	$ 29	$ 30
Electric Utility [Member]
Income Tax Benefits [Line Items]
Income tax benefits, to be returned to customers	$ 209
Tax benefit, distribution to customers, term	5 years
Gas Utility [Member]
Income Tax Benefits [Line Items]
Income tax benefits, to be returned to customers	$ 260
Tax benefit, distribution to customers, term	12 years