Commitments and Contingencies NSP-Minnesota - MEC Transactions (Details) - MEC Holdings LLC [Member] - Unregulated Operation [Member] $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) MW
Public Utilities, General Disclosures [Line Items]
Facility Output \| MW		760
PP&E Additions		$ 650
Southwest Generation [Domain]
Public Utilities, General Disclosures [Line Items]
PP&E Sale	$ 680

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration