Regulatory Matters - Conservation Improvement Program (CIP) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Regulatory Matters [Line Items]
Conservation Improvement Program Goal, Next Fiscal Year	$ 10.5
Conservation Improvement Program Goal, In 2 Years	10.7
Conservation Improvement Program Goal, In 3 Years	10.9
MPUC [Member] | CIP Consolidated Filing [Member] | Minnesota Power [Member]
Regulatory Matters [Line Items]
CIP Financial Incentive	$ 2.4	$ 2.8
MPUC [Member] | Minimum [Member]
Regulatory Matters [Line Items]
CIP Spending Minimum - Percentage	1.50%