Property, Plant and Equipment

SCE's property, plant and equipment included in the consolidated balance sheets is composed of the following:



	December 31,
(in millions)	2017			2016
Distribution	$	23,633		$	22,332
Transmission	13,127			12,549
Generation	3,468			3,376
General plant and other	4,534			4,633
Accumulated depreciation	(9,355		)	(9,000		)
	35,407			33,890
Construction work in progress	3,175			2,790
Nuclear fuel, at amortized cost	126			126
Total utility property, plant and equipment	$	38,708		$	36,806

Capitalized Software Costs

SCE capitalizes costs incurred during the application development stage of internal use software projects to property, plant, and equipment. SCE amortizes capitalized software costs ratably over the expected lives of the software, primarily ranging from 5 to 10 years and commencing upon operational use. Capitalized software costs, included in general plant and other above, were $1.1 billion and $1.4 billion at December 31, 2017 and 2016, respectively, and accumulated amortization was $0.6 billion and $0.8 billion, at December 31, 2017 and 2016, respectively. Amortization expense for capitalized software was $233 million, $249 million and $268 million in 2017, 2016 and 2015, respectively. At December 31, 2017, amortization expense is estimated to be $176 million, $127 million, $92 million, $62 million and $26 million for 2018 through 2022, respectively.

Jointly Owned Utility Projects

SCE owns undivided interests in several generating assets for which each participant provides its own financing. SCE's proportionate share of these assets is reflected in the consolidated balance sheets and included in the above table. SCE's proportionate share of expenses for each project is reflected in the consolidated statements of income. A portion of the investments in Palo Verde generating stations is included in regulatory assets on the consolidated balance sheets. For further information, see Note 10.

The following is SCE's investment in each asset as of December 31, 2017:



(in millions)	Plant in Service		Construction Work in Progress		Accumulated Depreciation		Nuclear Fuel (at amortized cost)		Net Book Value		Ownership Interest
Transmission systems:
Eldorado	$	237	$	14	$	24	$	—	$	227	59	%
Pacific Intertie	192		41		78		—		155		50	%
Generating station:
Palo Verde (nuclear)	2,001		52		1,557		126		622		16	%
Total	$	2,430	$	107	$	1,659	$	126	$	1,004

In addition, SCE has ownership interests in jointly owned power poles with other companies.