Income Taxes (Principal Components Of Deferred Income Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax assets
Tax loss and credit carryforwards	$ 483	$ 239
Net regulatory tax liability	372	385
Reserves and accruals	62	43
Total deferred income tax assets	917	667
Valuation allowance	(1)	(2)
Total deferred income tax assets, net of valuation allowance	916	665
Deferred income tax liabilities
Plant, property, and equipment	(2,287)	(2,033)
Employee benefits	(364)	(172)
Securitized costs	(53)	(59)
Gas inventory	(24)	(32)
Other	(51)	(24)
Total deferred income tax liabilities	(2,779)	(2,320)
Total net deferred income tax liabilities	(1,863)	(1,655)
Consumers Energy Company
Deferred income tax assets
Tax loss and credit carryforwards	216	20
Net regulatory tax liability	372	385
Reserves and accruals	24	24
Total deferred income tax assets, net of valuation allowance	612	429
Deferred income tax liabilities
Plant, property, and equipment	(2,230)	(1,995)
Employee benefits	(365)	(178)
Securitized costs	(53)	(59)
Gas inventory	(24)	(32)
Other	(34)	(29)
Total deferred income tax liabilities	(2,706)	(2,293)
Total net deferred income tax liabilities	$ (2,094)	$ (1,864)