Income Taxes (Narrative) (Details) - Consumers Energy Company [Member] - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Income Tax Benefits [Line Items]
Reduction of income tax expense	$ 20	$ 23
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