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Income Taxes - Effective Income Tax Rate (Details) | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Income Tax Disclosure [Abstract] |  |  |
Federal Statutory Rate | 21.00% | 21.00% | 21.00%
Increases (Decreases) in Tax from: |  |  |
State Taxes on Income, Net of Federal Tax | 4.70% | 4.00% | 3.40%
Production Tax Credits (PTCs) | (5.90%) | (1.10%) | 0.00%
Amortization of Excess Deferred Income Taxes | (2.00%) | (3.60%) | (3.20%)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax | (0.30%) | (0.90%) | (1.00%)
Allowance for Equity Funds Used During Construction | (0.10%) | (0.70%) | (0.50%)
Other, Net | (0.50%) | (1.30%) | (3.00%)
Effective Tax Rate | 16.90% | 17.40% | 16.70%

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