Regulatory Matters - Conservation Improvement Program (CIP) (Details) - MPUC [Member] - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| CIP Triennial Filing [Member] | Minnesota Power [Member] | |||
| Regulatory Matters [Line Items] | |||
| CIP Investment Goal | $ 10.5 | $ 10.3 | |
| CIP Actual Spending | 8.3 | 9.0 | $ 8.1 |
| CIP Investment Goal, Year Two | 10.5 | ||
| CIP Consolidated Filing [Member] | Minnesota Power [Member] | |||
| Regulatory Matters [Line Items] | |||
| CIP Financial Incentive | $ 2.8 | $ 3.0 | |
| Minimum [Member] | |||
| Regulatory Matters [Line Items] | |||
| CIP Spending Minimum - Percentage | 1.50% | ||