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Regulatory Matters - Four Corners and Cholla (Details) - APS $ in Millions |  |  | 9 Months Ended
--- | --- | --- | ---
Dec. 23, 2014 USD ($) | Dec. 30, 2013 USD ($) MW | Sep. 30, 2015 USD ($)
SCE | Four Corners Units 4 and 5 |  |  |
Business Acquisition [Line Items] |  |  |
Ownership interest acquired |  | 48.00% |
Settlement agreement, ACC approved rate adjustment, annualized customer impact | $ 57.1 |  |
Net receipt due to negotiation of alternate arrangement |  | $ 40.0 |
Capacity rights over the Arizona Transmission System assign to third-parties | MW |  | 1,555 |
Capacity rights related to marketing and trading group for transmission of the additional power received assign to third-parties | MW |  | 300 |
Four Corners cost deferral | SCE | Four Corners Units 4 and 5 |  |  |
Business Acquisition [Line Items] |  |  |
Regulatory assets, non-current |  |  | $ 72.0
Regulatory noncurrent asset amortization period |  |  | 10 years
Retired power plant costs |  |  |
Business Acquisition [Line Items] |  |  |
Net book value |  |  | $ 124.0

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