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Retirement Plans and Other Benefits Retirement Plans and Other Benefits - Additional Information (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Plan Design Changes [Abstract] |  |  |
Amount of other postretirement benefit trust assets for union employee medical costs | $ 186,000,000 |  |
Partnership funding commitments, contribution amount (up to) | 75,000,000 |  |
Partnership funding commitments, funded amount | $ 62,000,000 |  |
Pension Benefits |  |  |
Plan Design Changes [Abstract] |  |  |
Expected long-term return on plan assets for next fiscal year (as a percent) | 6.25% |  |
Contributions |  |  |
Employer contributions | $ 50,000,000 | $ 100,000,000 | $ 100,000,000
Minimum contributions under MAP-21 |  |  |
Minimum contributions under MAP-21 | 0 |  |
Voluntary employer contributions over next three years (up to) | $ 350,000,000 |  |
Other Benefits |  |  |
Plan Design Changes [Abstract] |  |  |
Expected long-term return on plan assets for next fiscal year (as a percent) | 5.55% |  |
Contributions |  |  |
Employer contributions | $ 0 | 353,000 |
Employee savings plan benefits |  |  |
Retiree medical cost reimbursement | 72,000,000 |  |
Pinnacle West |  |  |
Employee savings plan benefits |  |  |
Expenses recorded for the defined contribution savings plan | $ 11,000,000 | 10,000,000 | 10,000,000
ARIZONA PUBLIC SERVICE COMPANY |  |  |
Employee savings plan benefits |  |  |
APS's employees share of total cost of the plans (as a percent) | 99.00% |  |
ARIZONA PUBLIC SERVICE COMPANY | Other Benefits |  |  |
Contributions |  |  |
Employer contributions | $ 0 | $ 1,000,000 | $ 1,000,000

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- Definition Defined Benefit Plan - Amount of Other Postretirement Benefit Trust Assets for Union Employee Medical Costs + References No definition available. + Details
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- Definition An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation during next fiscal year. + References No definition available. + Details
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