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Operations and Significant Accounting Policies - Revenue - Nature of Revenue Streams (Continued) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Capitalized Contract Cost, Amortization | $ 2.7 | $ 2.6
Revenue, Performance Obligation, Description of Payment Terms | Payment terms and conditions vary across our businesses. Aside from taconite-producing Large Power Customers, payment terms generally require payment to be made within 15 to 30 days from the end of the period that the service has been rendered. In the case of its taconite-producing Large Power Customers, as permitted by the MPUC, Minnesota Power requires weekly payments for electric usage based on monthly energy usage estimates. |
Long-term Contract with Customer [Member] | Regulated Operations [Member] | Industrial Customers [Member] | Industrial [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year |
Long-term Contract with Customer [Member] | Regulated Operations [Member] | Industrial Customers [Member] | Industrial [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year |
Revenue, Remaining Performance Obligation, Amount | $ 50.0 |
Long-term Contract with Customer [Member] | Regulated Operations [Member] | Industrial Customers [Member] | Industrial [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01 |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year |
Revenue, Remaining Performance Obligation, Amount | $ 50.0 |
Long-term Contract with Customer [Member] | Regulated Operations [Member] | Industrial Customers [Member] | Industrial [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year |
Revenue, Remaining Performance Obligation, Amount | $ 50.0 |
Long-term Contract with Customer [Member] | Regulated Operations [Member] | Industrial Customers [Member] | Industrial [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01 |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year |
Revenue, Remaining Performance Obligation, Amount | $ 50.0 |
Long-term Contract with Customer [Member] | Regulated Operations [Member] | Industrial Customers [Member] | Industrial [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01 |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year |
Revenue, Remaining Performance Obligation, Amount | $ 15.0 |
Long-term Contract with Customer [Member] | Regulated Operations [Member] | Industrial Customers [Member] | Industrial [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01 |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 3 years |
Revenue, Remaining Performance Obligation, Amount | $ 30.0 |

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