Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Long-Term Borrowings and Other Financing Instruments (Details) - PSCo - Bonds [Member] - Series Due September 15, 2049 [Domain] $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 400
Debt Instrument, Interest Rate, Stated Percentage	4.05%
Maturity Date	Sep. 15, 2049