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%