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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
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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

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