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- Definition

Asset Purchase Agreement, Operating and Maintenance Cost Reimbursement Receivable

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- Definition

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

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- Definition

Asset Purchase Agreement, Proceeds from Operating an Maintenance Cost Reimbursement

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- Definition

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

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- Definition

Environmental Matters [Abstract]

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Guarantor Obligations, Number of Parental Guarantees

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- Definition

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

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- Definition

Prepaid Energy Related Inventory, Coal

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- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

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

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

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

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

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Commitments and Contingencies - Environmental Matters and Financial Assurances (Details) $ in Millions					12 Months Ended
	Jul. 03, 2018 USD ($)	Jun. 29, 2018 USD ($)	Jun. 13, 2017 USD ($)	Jul. 06, 2016 guarantee	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 12, 2018 USD ($)
Payment Guarantee
Financial Assurances
Number of parental guarantees \| guarantee				5
Letter of credit \| ARIZONA PUBLIC SERVICE COMPANY
Financial Assurances
Outstanding letters of credit					$ 0.2
Equity Lessors Sale Leaseback Letter of Credit \| ARIZONA PUBLIC SERVICE COMPANY
Financial Assurances
Outstanding letters of credit					17.0
Four Corners \| NTEC
Environmental Matters [Abstract]
Option to purchase, ownership interest (as a percent)	7.00%			7.00%
Payment received for coal supply agreement	$ 70.0
Four Corners \| 4CA
Environmental Matters [Abstract]
Percentage share cost of control	7.00%			7.00%
Four Corners \| Coal Supply Agreement Arbitration
Environmental Matters [Abstract]
Damages sought			$ 30.0
Litigation settlement		$ 45.0
Four Corners \| Coal Supply Agreement Arbitration \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Damages sought			$ 17.0
Litigation settlement		$ 34.0
Prepaid energy related inventory, coal							$ 24.0
Four Corners \| Coal Supply Agreement Arbitration \| NTEC
Environmental Matters [Abstract]
Option to purchase, ownership interest (as a percent)				7.00%
Four Corners \| Coal Supply Agreement Arbitration \| 4CA
Environmental Matters [Abstract]
Payment received for coal supply agreement						$ 10.0
Operating and maintenance cost reimbursement receivable					10.0	$ 20.0
Regional Haze Rules \| Navajo Generating Station \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Expected environmental cost					$ 200.0
Regional Haze Rules \| Four Corners Units 4 and 5 \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Percentage share cost of control					63.00%
Expected environmental cost					$ 400.0
Regional Haze Rules \| Four Corners Units 4 and 5 \| Four Corners \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Additional expected environment cost					$ 45.0
Regional Haze Rules \| Four Corners Units 4 and 5 \| Natural Gas Tolling Letter of Credit \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Additional percentage share of cost of control					7.00%
Coal Combustion Waste \| Four Corners \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Additional expected environment cost					$ 22.0
Coal Combustion Waste \| Navajo Generating Station \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Additional expected environment cost					1.0
Coal Combustion Waste \| Cholla and Four Corners \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Additional expected environment cost					5.0
Coal Combustion Waste \| Minimum \| Cholla \| ARIZONA PUBLIC SERVICE COMPANY
Environmental Matters [Abstract]
Additional expected environment cost					$ 20.0
El Paso's Interest in Four Corners \| 4CA
Financial Assurances
Ownership interest acquired (as a percent)				7.00%	7.00%