Income Taxes (Principal Components Of Deferred Income Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Employee benefits	$ (158)	$ (127)
Gas inventory	(65)	(96)
Property, plant and equipment	(2,902)	(2,429)
Net regulatory tax liability	27	50
Reserves and accruals	69	59
Securitized costs	(118)	(122)
Tax loss and credit carryforwards	871	657
Other	(6)	(5)
Gross Deferred Tax Liabilities	(2,282)	(2,013)
Less: valuation allowance	(5)	(4)
Total net deferred income tax liabilities	(2,287)	(2,017)
Deferred tax assets, net of valuation reserves	962	762
Deferred tax liabilities	(3,249)	(2,779)
Consumers Energy Company [Member]
Employee benefits	(181)	(156)
Gas inventory	(65)	(96)
Property, plant and equipment	(2,924)	(2,457)
Net regulatory tax liability	27	50
Reserves and accruals	37	30
Securitized costs	(118)	(122)
Tax loss and credit carryforwards	190	46
Other	(8)	(5)
Total net deferred income tax liabilities	(3,042)	(2,710)
Deferred tax assets, net of valuation reserves	254	126
Deferred tax liabilities	$ (3,296)	$ (2,836)