Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Benefits [Line Items]
Interest and penalties	$ 0	$ 0	$ 0
IRS audit, adjustments to income tax expense	0
Consumers Energy Company [Member]
Income Tax Benefits [Line Items]
Reduction of income tax expense	39
Interest and penalties	0	0	0
IRS audit, adjustments to income tax expense	0
Electric Utility [Member] | Consumers Energy Company [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] | Consumers Energy Company [Member]
Income Tax Benefits [Line Items]
Income tax benefits, to be returned to customers	$ 260
Tax benefit, distribution to customers, term	12 years