Income Taxes (Narrative) (Details) (Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Income Tax Benefits [Line Items]
Reduction of income tax expense	$ 14
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