Income Taxes (Principal Components Of Deferred Income Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Employee benefits	$ (127)	$ (72)
Gas inventory	(96)	(117)
Property, plant and equipment	(2,429)	(2,217)
Net regulatory tax liability	50	65
Reserves and accruals	59	63
Securitized costs	(122)	(144)
Tax loss and credit carryforwards	657	676
Other	(5)
Gross Deferred Tax Liabilities	(2,013)	(1,746)
Less: valuation allowance	(4)	(2)
Total net deferred income tax liabilities	(2,017)	(1,748)
Deferred tax assets, net of valuation reserves	762	802
Deferred tax liabilities	(2,779)	(2,550)
Consumers Energy Company [Member]
Employee benefits	(156)	(103)
Gas inventory	(96)	(117)
Property, plant and equipment	(2,457)	(2,263)
Net regulatory tax liability	50	65
Reserves and accruals	30	34
Securitized costs	(122)	(144)
Tax loss and credit carryforwards	46	45
Other	(5)	(2)
Gross Deferred Tax Liabilities	(2,710)	(2,485)
Less: valuation allowance		(1)
Total net deferred income tax liabilities	(2,710)	(2,486)
Deferred tax assets, net of valuation reserves	126	143
Deferred tax liabilities	$ (2,836)	$ (2,629)