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