Borrowings and Other Financing Instruments (Details) - Series Due May 1, 2051 [Domain] - Bonds [Member]	May 26, 2020 USD ($)
Debt Disclosure [Abstract]
Debt Instrument, Face Amount	$ 100,000,000
Short-term Debt [Line Items]
Debt Instrument, Face Amount	$ 100,000,000
NSP-Wisconsin [Member]
Debt Disclosure [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	305.00%
Short-term Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	305.00%

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant