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Income Taxes (Schedule Of Effective Income Rate Reconciliation) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020
Income Taxes [Line Items] |  |  |
U.S. federal income tax rate | 21.00% | 21.00% |
Increase (decrease) in income taxes from: |  |  |
State and local income taxes, net of federal effect | 5.10% | 4.60% |
TCJA excess deferred taxes | (5.30%) | (3.90%) |
Production tax credits | (4.70%) | (2.80%) |
Accelerated flow-through of regulatory tax benefits | (3.00%) | (1.50%) |
Research and development tax credits, net | (0.30%) | (3.40%) |
Refund of alternative minimum tax sequestration | 0.00% | (3.30%) |
Other, net | 0.20% | (0.70%) |
Effective tax rate | 13.00% | 10.00% |
Refund of alternative minimum tax sequestration |  |  | $ (9)
Consumers Energy Company |  |  |
Income Taxes [Line Items] |  |  |
U.S. federal income tax rate | 21.00% | 21.00% |
Increase (decrease) in income taxes from: |  |  |
State and local income taxes, net of federal effect | 5.10% | 4.90% |
TCJA excess deferred taxes | (5.10%) | (3.40%) |
Production tax credits | (2.60%) | (1.40%) |
Accelerated flow-through of regulatory tax benefits | (3.70%) | (1.90%) |
Research and development tax credits, net | (0.20%) | (3.10%) |
Other, net | (0.20%) | (0.30%) |
Effective tax rate | 14.30% | 15.80% |
Research Tax Credit Carryforward |  |  |
Increase (decrease) in income taxes from: |  |  |
Increase (decrease) in tax credit carryforward |  |  | 9
Research Tax Credit Carryforward | Consumers Energy Company |  |  |
Increase (decrease) in income taxes from: |  |  |
Increase (decrease) in tax credit carryforward |  |  | $ 8

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