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Regulatory Matters - Four Corners, Cholla and Navajo Plant (Details) - USD ($) $ in Millions |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 13, 2017 | Dec. 23, 2014 | Dec. 30, 2013 | Jul. 31, 2012 | Jun. 30, 2016 | Dec. 31, 2016 | Feb. 13, 2017 | Dec. 31, 2015
Acquisition |  |  |  |  |  |  |  |
Regulatory asset amortization period |  |  |  | 3 years |  |  |  |
Retired power plant costs | APS |  |  |  |  |  |  |  |
Acquisition |  |  |  |  |  |  |  |
Regulatory asset, net book value |  |  |  |  |  | $ 116.0 |  |
SCE | Four Corners | APS |  |  |  |  |  |  |  |
Acquisition |  |  |  |  |  |  |  |
Regulatory assets |  |  |  |  |  |  |  | $ 12.0
Transmission termination agreement net receipt due to negotiation of alternate arrangement |  |  | $ 40.0 |  |  |  |  |
Regulatory assets, write of amount |  |  |  |  | $ 12.0 |  |  |
Four Corners Units 4 and 5 | SCE | APS |  |  |  |  |  |  |  |
Acquisition |  |  |  |  |  |  |  |
Ownership interest acquired |  |  | 48.00% |  |  |  |  |
Settlement agreement, ACC approved rate adjustment, annualized customer impact |  | $ 57.1 |  |  |  |  |  |
Four Corners Units 4 and 5 | SCE | Four Corners cost deferral | APS |  |  |  |  |  |  |  |
Acquisition |  |  |  |  |  |  |  |
Regulatory assets |  |  |  |  |  | $ 64.0 |  |
Regulatory asset amortization period |  |  |  |  |  | 10 years |  |
Subsequent Event | Navajo Plant | APS |  |  |  |  |  |  |  |
Acquisition |  |  |  |  |  |  |  |
Asset net book value |  |  |  |  |  |  | $ 108.0 |
Subsequent Event | Compromise Proposal to meet Environmental and Emissions Standards and Rules | ACC | APS |  |  |  |  |  |  |  |
Acquisition |  |  |  |  |  |  |  |
Number of days to file a petition | 60 days |  |  |  |  |  |  |

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