Asset Purchase Agreement, Additional Percentage Share of Cost of Control

No definition available.

Name:	pnw_AssetPurchaseAgreementAdditionalPercentageShareofCostofControl
Namespace Prefix:	pnw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Asset Purchase Agreement, Operating and Maintenance Cost Reimbursement Receivable

+ References

No definition available.

+ Details

Name:	pnw_AssetPurchaseAgreementOperatingandMaintenanceCostReimbursementReceivable
Namespace Prefix:	pnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Asset Purchase Agreement, Option to Purchase, Ownership Interest, Percentage

+ References

No definition available.

+ Details

Name:	pnw_AssetPurchaseAgreementOptiontoPurchaseOwnershipInterestPercentage
Namespace Prefix:	pnw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Asset Purchase Agreement, Proceeds from Operating an Maintenance Cost Reimbursement

+ References

No definition available.

+ Details

Name:	pnw_AssetPurchaseAgreementProceedsfromOperatinganMaintenanceCostReimbursement
Namespace Prefix:	pnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Asset Purchase Agreement, Site Contingency, Increase in Loss Exposure Not Accrued, Best Estimate

+ References

No definition available.

+ Details

Name:	pnw_AssetPurchaseAgreementSiteContingencyIncreaseinLossExposureNotAccruedBestEstimate
Namespace Prefix:	pnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

Name:	pnw_FinancialAssurancesAbstract
Namespace Prefix:	pnw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Guarantor Obligations, Number of Parental Guarantees

+ References

No definition available.

+ Details

Name:	pnw_GuarantorObligationsNumberofParentalGuarantees
Namespace Prefix:	pnw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of share of the cost of control acquired by the entity.

+ References

No definition available.

+ Details

Name:	pnw_PercentageOfShareOfCostOfControl
Namespace Prefix:	pnw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Prepaid Energy Related Inventory, Coal

+ References

No definition available.

+ Details

Name:	pnw_PrepaidEnergyRelatedInventoryCoal
Namespace Prefix:	pnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Supply Agreement [Abstract]

+ References

No definition available.

+ Details

Name:	pnw_SupplyAgreementAbstract
Namespace Prefix:	pnw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Surety Bonds Expiring, Amount

+ References

No definition available.

+ Details

Name:	pnw_SuretyBondsExpiringAmount
Namespace Prefix:	pnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementAmountAwardedToOtherParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

+ Details

Name:	us-gaap_LossContingencyDamagesSoughtValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SiteContingencyLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Best estimate of the loss exposure for reasonably possible environmental contingencies at an individual site for which no accrual has been recorded.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 10
-Subparagraph (c),(d)(2)
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 10
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

+ Details

Name:	us-gaap_SiteContingencyLossExposureNotAccruedBestEstimate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_LitigationCaseAxis=pnw_CoalSupplyAgreementArbitrationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=pnw_FourCornersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=pnw_ArizonaPublicServiceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=pnw_LettersofCreditExpiringin2018and2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=pnw_LettersofCreditExpiringin2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=pnw_A4CAcquisitionLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=pnw_FourCornersUnits4And5Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=pnw_NavajoTransitionalEnergyCompanyLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationContingencyAxis=pnw_RegionalHazeRulesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=pnw_NaturalGasTollingLetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=pnw_FourCornersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=pnw_NavajoGeneratingStationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationContingencyAxis=pnw_CoalCombustionWasteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=pnw_ChollaandFourCornersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=pnw_ChollaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_PaymentGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingencies - Environmental Matters and Financial Assurances (Details) $ in Millions					9 Months Ended	12 Months Ended
	Jul. 03, 2018 USD ($)	Jun. 29, 2018 USD ($)	Jun. 13, 2017 USD ($)	Jul. 06, 2016 guarantee	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 12, 2018 USD ($)
Coal Supply Agreement Arbitration \| Four Corners
Four Corners Coal Supply Agreement
Damages sought			$ 30.0
Settlement amount		$ 45.0
APS \| Coal Supply Agreement Arbitration \| Four Corners
Four Corners Coal Supply Agreement
Damages sought			$ 17.0
Settlement amount		$ 34.0
Coal advance purchase							$ 24.0
APS \| Letters of Credit Expiring in 2018, 2019
Financial Assurances
Outstanding letters of credit					$ 0.2
APS \| Letters of Credit Expiring in 2019
Financial Assurances
Surety bonds expiring, amount					$ 36.0
4C Acquisition, LLC \| Four Corners Units 4 and 5
Environmental Matters
Percentage of share of cost of control					7.00%
4C Acquisition, LLC \| Four Corners
Environmental Matters
Percentage of share of cost of control				7.00%
4C Acquisition, LLC \| Coal Supply Agreement Arbitration \| Four Corners
Four Corners Coal Supply Agreement
Proceeds from operating and maintenance cost reimbursement						$ 10.0
Reimbursement payments due to 4CA					$ 10.0	$ 20.0
NTEC \| Four Corners
Four Corners Coal Supply Agreement
Option to purchase ownership interest (as a percent)	7.00%			7.00%
Proceeds from operating and maintenance cost reimbursement	$ 70.0
NTEC \| Coal Supply Agreement Arbitration \| Four Corners
Four Corners Coal Supply Agreement
Option to purchase ownership interest (as a percent)				7.00%
Regional Haze Rules \| APS \| Four Corners Units 4 and 5
Environmental Matters
Percentage of share of cost of control					63.00%
Expected environmental cost					$ 400.0
Regional Haze Rules \| APS \| Natural gas tolling contract obligations \| Four Corners Units 4 and 5
Environmental Matters
Additional percentage share of cost of control					7.00%
Regional Haze Rules \| APS \| Four Corners \| Four Corners Units 4 and 5
Environmental Matters
Site contingency increase in loss exposure not accrued, best estimate					$ 45.0
Regional Haze Rules \| APS \| Navajo Plant
Environmental Matters
Expected environmental cost					200.0
Coal combustion waste \| APS \| Four Corners
Environmental Matters
Site contingency increase in loss exposure not accrued, best estimate					22.0
Coal combustion waste \| APS \| Navajo Plant
Environmental Matters
Site contingency increase in loss exposure not accrued, best estimate					1.0
Coal combustion waste \| APS \| Cholla and Four Corners
Environmental Matters
Site contingency increase in loss exposure not accrued, best estimate					5.0
Minimum \| Coal combustion waste \| APS \| Cholla
Environmental Matters
Site contingency increase in loss exposure not accrued, best estimate					$ 20.0
Payment Guarantee
Financial Assurances
Number of parental guarantees \| guarantee				5