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Fair Value Measurements - Significant Unobservable Inputs Used to Value Level 3 Instruments (Details 2) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Mar. 31, 2015 | Dec. 31, 2014
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | $ 33 us-gaap_AssetsFairValueDisclosure | $ 33 us-gaap_AssetsFairValueDisclosure
Liabilities | 82 us-gaap_LiabilitiesFairValueDisclosure | 74 us-gaap_LiabilitiesFairValueDisclosure
Electricity forward contracts |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | 31 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember | 30 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember
Liabilities | 60 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember | 56 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember
Electricity forward contracts | Minimum | Discounted cash flows |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | 18.88 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember | 19.51 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember
Electricity forward contracts | Maximum | Discounted cash flows |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | 46.54 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember | 56.72 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember
Electricity forward contracts | Weighted Average | Discounted cash flows |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | 30.49 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember | 35.27 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = pnw_ElectricityContractsMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember
Option Contracts |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember | 0 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember
Liabilities | 15 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember | 15 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember
Option Contracts | Minimum | Option model |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | 30.24 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 32.14 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Natural gas forward price (per MMbtu) | 2.35 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 3.18 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Electricity price volatilities (as a percent) | 27.00%pnw_FairValueInputsImpliedElectricityVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 23.00%pnw_FairValueInputsImpliedElectricityVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Natural gas price volatilities (as a percent) | 26.00%pnw_FairValueInputsImpliedGasPriceVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 23.00%pnw_FairValueInputsImpliedGasPriceVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Option Contracts | Maximum | Option model |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | 60.45 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 66.09 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Natural gas forward price (per MMbtu) | 2.88 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 3.29 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Electricity price volatilities (as a percent) | 86.00%pnw_FairValueInputsImpliedElectricityVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 63.00%pnw_FairValueInputsImpliedElectricityVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Natural gas price volatilities (as a percent) | 43.00%pnw_FairValueInputsImpliedGasPriceVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 41.00%pnw_FairValueInputsImpliedGasPriceVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Option Contracts | Weighted Average | Option model |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Electricity forward price (per MWh) | 41.81 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 45.83 pnw_FairValueInputsElectricityForwardPricePerMegawattHours / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Natural gas forward price (per MMbtu) | 2.83 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 3.25 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Electricity price volatilities (as a percent) | 54.00%pnw_FairValueInputsImpliedElectricityVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 41.00%pnw_FairValueInputsImpliedElectricityVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Natural gas price volatilities (as a percent) | 32.00%pnw_FairValueInputsImpliedGasPriceVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember | 31.00%pnw_FairValueInputsImpliedGasPriceVolatilities / us-gaap_FairValueByLiabilityClassAxis = us-gaap_CommodityOptionMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = pnw_OptionModelValuationTechniqueMember
Natural gas forward contracts |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Assets | 2 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember | 3 us-gaap_AssetsFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember
Liabilities | $ 7 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember | $ 3 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember
Natural gas forward contracts | Minimum | Discounted cash flows |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Natural gas forward price (per MMbtu) | 2.30 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember | 2.98 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember
Natural gas forward contracts | Maximum | Discounted cash flows |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Natural gas forward price (per MMbtu) | 3.59 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember | 4.13 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember
Natural gas forward contracts | Weighted Average | Discounted cash flows |  |
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments |  |
Natural gas forward price (per MMbtu) | 3.01 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember | 3.45 pnw_FairValueInputsGasForwardPricePerMetricMillionBritishThermalUnits / us-gaap_FairValueByLiabilityClassAxis = pnw_NaturalGasContractsMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember

X
- Definition Represents the electricity forward price per Megawatt Hours, used as an input to measure fair value. + References No definition available. + Details
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- Definition Represents the gas price per Metric Million British Thermal Units, used as an input to measure fair value. + References No definition available. + Details
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- Definition Represents the percentage of implied electricity volatilities. + References No definition available. + Details
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- Definition Represents the percentage of implied electricity natural gas price volatilities. + References No definition available. + Details
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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