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Borrowings and Other Financing Instruments Long-Term Borrowings (Details) - Bonds [Member] - USD ($) | Jul. 19, 2021 | Mar. 23, 2021 | Mar. 02, 2021 | Mar. 01, 2021
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PSCo | Series Due June 15, 2031 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Instrument, Face Amount |  |  |  | $ 750,000,000
Debt Instrument, Interest Rate, Stated Percentage |  |  |  | 1.875%
SPS | Series Due 2050 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Instrument, Face Amount |  |  | $ 250,000,000 |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.15% |
NSP-Wisconsin | Series Due May 1, 2051 [Domain] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Instrument, Face Amount | $ 100,000,000 |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 2.82% |  |  |
NSP-Minnesota | Series Due April 1, 2031 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Instrument, Face Amount |  | $ 425,000,000 |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 2.25% |  |
NSP-Minnesota | Series Due April 1, 2052 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt Instrument, Face Amount |  | $ 425,000,000 |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 3.20% |  |

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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