Borrowings and Other Financing Instruments Long-Term Borrowings (Details) - Bonds [Member] $ in Millions |
Sep. 30, 2019
USD ($)
|
|---|---|
| PSCo | Series Due Sept. 15, 2049 [Domain] | |
| Debt Instrument [Line Items] | |
| Debt Instrument, Face Amount | $ 400 |
| Debt Instrument, Interest Rate, Stated Percentage | 4.05% |
| PSCo | Series Due March 1, 2050 [Domain] | |
| Debt Instrument [Line Items] | |
| Debt Instrument, Face Amount | $ 550 |
| Debt Instrument, Interest Rate, Stated Percentage | 3.20% |
| XCEL ENERGY INC [Member] | Series Due June 15, 2028 [Domain] | |
| Debt Instrument [Line Items] | |
| Debt Instrument, Face Amount | $ 130 |
| Debt Instrument, Interest Rate, Stated Percentage | 4.00% |
| SPS | Series Due June 15, 2049 [Domain] | |
| Debt Instrument [Line Items] | |
| Debt Instrument, Face Amount | $ 300 |
| Debt Instrument, Interest Rate, Stated Percentage | 3.75% |
| NSP Minnesota [Member] | Series Due March 1, 2050 [Domain] | |
| Debt Instrument [Line Items] | |
| Debt Instrument, Face Amount | $ 600 |
| Debt Instrument, Interest Rate, Stated Percentage | 2.90% |