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Commitments and Contingencies, Variable Interest Entities (Details)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
MW
Independent Power Producing Entities    
Purchased Power Agreements [Abstract]    
Generating capacity (in MW) 1,802psco_GeneratingCapacityUnderLongTermPurchasedPowerAgreements
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember		 1,441psco_GeneratingCapacityUnderLongTermPurchasedPowerAgreements
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember
Maximum [Member]    
Purchased Power Agreements [Abstract]    
Purchase Power Agreement Duration, Maximum 2032