Income Taxes (Principal Components Of Deferred Income Tax Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Employee benefits	$ (72)	$ (99)
Gas inventory	(117)	(130)
Property, plant and equipment	(2,217)	(1,856)
Net regulatory tax liability	65	86
Reserves and accruals	63	57
Securitized costs	(144)	(190)
Tax loss and credit carryforwards	676	629
Other		15
Gross Deferred Tax Liabilities	(1,746)	(1,488)
Less: valuation allowance	(2)	(2)
Total net deferred income tax liabilities	(1,748)	(1,490)
Deferred tax assets, net of valuation reserves	802	785
Deferred tax liabilities	(2,550)	(2,275)
Consumers Energy Company [Member]
Employee benefits	(103)	(119)
Gas inventory	(117)	(130)
Property, plant and equipment	(2,263)	(1,911)
Net regulatory tax liability	65	86
Reserves and accruals	34	31
Securitized costs	(144)	(190)
Tax loss and credit carryforwards	45	48
Other	(2)	16
Gross Deferred Tax Liabilities	(2,485)	(2,169)
Less: valuation allowance	(1)	(1)
Total net deferred income tax liabilities	(2,486)	(2,170)
Deferred tax assets, net of valuation reserves	143	180
Deferred tax liabilities	$ (2,629)	$ (2,350)