pre_text: (9) Property, Plant and Equipment Net property, plant and equipment is composed of the following: (1) Fiber, conduit and other outside plant consists of fiber and metallic cable, conduit, poles and other supporting structures. 2) Central office and other network electronics consists of circuit and packet switches, routers, transmission electronics and electronics providing service to customers. (3) Support assets consist of buildings, cable landing stations, data centers, computers and other administrative and support equipment. (4) Construction in progress includes inventory held for construction and property of the aforementioned categories that has not been placed in service as it is still under construction. We recorded depreciation expense of $3.1 billion, $3.3 billion and $2.7 billion for the years ended December 31, 2019, 2018 and 2017, respectively.
table: Depreciable Lives As of December 31
table: 2019 2018
table: (Dollars in millions)
table: Land N/A $867 871
table: Fiber, conduit and other outside plant(1) 15-45 years 24,666 23,936
table: Central office and other network electronics(2) 3-10 years 19,608 18,736
table: Support assets(3) 3-30 years 7,984 8,020
table: Construction in progress(4) N/A 2,300 1,704
table: Gross property, plant and equipment 55,425 53,267
table: Accumulated depreciation (29,346) (26,859)
table: Net property, plant and equipment $26,079 26,408
question: Analyse this data from a financial earnings document. What is the average net property, plant and equipment?