Stock-Based Compensation (Schedule Of Compensation Cost For Share-Based Payment Arrangements, Allocation Of Share-Based Compensation Costs By Plan) (Details) - Restricted stock - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares that vested during the year	$ 22	$ 26	$ 27
Compensation expense recognized	11	22	17
Income tax benefit recognized	3	1	1
Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares that vested during the year	21	25	26
Compensation expense recognized	10	21	16
Income tax benefit recognized	$ 3	$ 1	$ 1

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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