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Commitments and Contingencies, Environmental Contingencies (Details) (Regional Haze Rules, USD $)
In Millions, unless otherwise specified
Dec. 31, 2010
Boiler
Kiln
Group
Mar. 31, 2015
Environmental Requirements [Abstract]    
Number of environmental groups who petitioned the U.S. Department of the Interior 2psco_NumberOfEnvironmentalGroupsWhoPetitionedTheU.S.DepartmentOfTheInterior  
Number of coal-fired boilers in Colorado 12psco_NumberOfCoalFiredBoilersInColorado  
Number of coal-fired cement kilns in Colorado 1psco_NumberOfCoalFiredCementKilnsInColorado  
Capital Addition Purchase Commitments    
Environmental Requirements [Abstract]    
Liability for estimated cost to comply with regulation   $ 82.4psco_LiabilityForEstimatedCostToComplyWithRegulation
/ psco_EnvironmentalRegulationAxis
= psco_RegionalHazeRulesMember
/ us-gaap_UnrecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis
= us-gaap_CapitalAdditionsMember