Regulatory Matters - Nemadji Trail Energy Center (Details) - Natural Gas-fired [Member]	9 Months Ended
Sep. 30, 2021 MW
Nemadji Trail Energy Center [Member]
Regulatory Matters [Line Items]
Generating Capacity to be Jointly Owned (MW)	600
Natural Gas PPA [Member] \| Resource Package [Member] \| MPUC [Member] \| Minnesota Power [Member]
Regulatory Matters [Line Items]
Expected Output Entitlement	20.00%

Share of plant output being purchased under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.D)
-URI http://asc.fasb.org/extlink&oid=122136240&loc=d3e659339-123030

Name:	us-gaap_LongTermContractForPurchaseOfElectricPowerShareOfPlantOutputBeingPurchased
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration