Regulatory Matters - Four Corners, Cholla and Navajo Plant (Details) - APS - USD ($) $ in Millions			3 Months Ended	12 Months Ended
	Dec. 23, 2014	Dec. 30, 2013	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2015
Retired power plant costs
Acquisition
Regulatory asset, net book value				$ 105.0
Navajo Plant
Acquisition
Regulatory asset, net book value				99.0
SCE | Four Corners
Acquisition
Regulatory assets					$ 12.0
Regulatory assets, write of amount			$ 12.0
Four Corners Units 4 and 5 | SCE
Acquisition
Ownership interest acquired (as a percent)		48.00%
Settlement agreement, ACC approved rate adjustment, annualized customer impact	$ 57.1
Transmission termination agreement net receipt due to negotiation of alternate arrangement		$ 40.0
Four Corners Units 4 and 5 | SCE | Four Corners cost deferral
Acquisition
Regulatory assets				$ 56.0
Amortization period				10 years