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Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
MWh
Dec. 31, 2013
MWh
Credit Concentration Risk [Member]    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure 10psco_Numberofmostsignificantcounterpartiesforwholesaletradingandnontradingcommodityactivitieswithcreditexposure
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember		  
Credit Concentration Risk [Member] | Investment Grade Ratings from Standard & Poor's, Moody's, or Fitch Ratings [Member]    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure 7psco_Numberofmostsignificantcounterpartiesforwholesaletradingandnontradingcommodityactivitieswithcreditexposure
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ psco_CreditQualityIndicatorAxis
= psco_InvestmentGradeRatingsFromStandardPoorsMoodysOrFitchRatingsMember		  
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties 35.3psco_WholesaleTradingAndNonTradingCommodityCreditExposureForMostSignificantCounterparties
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ psco_CreditQualityIndicatorAxis
= psco_InvestmentGradeRatingsFromStandardPoorsMoodysOrFitchRatingsMember		  
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths) 43.00%psco_PercentageOfWholesaleTradingAndNonTradingCommodityCreditExposureForMostSignificantCounterparties
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ psco_CreditQualityIndicatorAxis
= psco_InvestmentGradeRatingsFromStandardPoorsMoodysOrFitchRatingsMember		  
Credit Concentration Risk [Member] | No Investment Grade Ratings from External Credit Rating Agencies [Member]    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure 3psco_Numberofmostsignificantcounterpartiesforwholesaletradingandnontradingcommodityactivitieswithcreditexposure
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ psco_CreditQualityIndicatorAxis
= psco_NoInvestmentGradeRatingsFromExternalCreditRatingAgenciesMember		  
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties 31.0psco_WholesaleTradingAndNonTradingCommodityCreditExposureForMostSignificantCounterparties
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ psco_CreditQualityIndicatorAxis
= psco_NoInvestmentGradeRatingsFromExternalCreditRatingAgenciesMember		  
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths) 38.00%psco_PercentageOfWholesaleTradingAndNonTradingCommodityCreditExposureForMostSignificantCounterparties
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ psco_CreditQualityIndicatorAxis
= psco_NoInvestmentGradeRatingsFromExternalCreditRatingAgenciesMember		  
Electric Commodity [Member]    
Gross Notional Amounts of Commodity Forwards and Options [Abstract]    
Derivative, Nonmonetary Notional amount 0invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= psco_ElectricCommodityMember		 [1],[2] 326,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= psco_ElectricCommodityMember		 [1],[2]
Natural Gas Commodity [Member]    
Gross Notional Amounts of Commodity Forwards and Options [Abstract]    
Derivative, Nonmonetary Notional amount 735,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= psco_NaturalGasCommodityMember		 [1],[2] 6,398,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= psco_NaturalGasCommodityMember		 [1],[2]
Vehicle Fuel Commodity [Member]    
Gross Notional Amounts of Commodity Forwards and Options [Abstract]    
Derivative, Nonmonetary Notional amount 127,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= psco_VehicleFuelCommodityMember		 [1],[2] 217,000invest_DerivativeNonmonetaryNotionalAmount
/ us-gaap_DerivativeByNatureAxis
= psco_VehicleFuelCommodityMember		 [1],[2]
[1] Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.
[2] Amounts are not reflective of net positions in the underlying commodities.