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Property, Plant and Equipment
 12 Months Ended
Dec. 31, 2019
Property, Plant and Equipment [Abstract]  
Property, Plant and Equipment
Note 9 Property, Plant and Equipment
Property, plant and equipment in service and under construction, and related accumulated depreciation and amortization, as of December 31, 2019 and 2018, were as follows:
December 31,
Useful Lives (Years)
 
2019
 
2018
(Dollars in millions)
 
 
 

 
 

Land
 N/A
 
$
35

 
$
35

Buildings
20
 
295

 
296

Leasehold and land improvements
 1-30
 
1,280

 
1,210

Cell site equipment
 7-25
 
3,708

 
3,460

Switching equipment
 5-8
 
1,051

 
1,018

Office furniture and equipment
 3-5
 
280

 
285

Other operating assets and equipment
 3-5
 
48

 
51

System development
 1-7
 
1,238

 
1,149

Work in process
 N/A
 
358

 
274

Total property, plant and equipment, gross
 
 
8,293

 
7,778

Accumulated depreciation and amortization
 
 
(6,086
)
 
(5,576
)
Total property, plant and equipment, net
 
 
$
2,207

 
$
2,202


Depreciation and amortization expense totaled $689 million, $627 million and $604 million in 2019, 2018 and 2017, respectively. In 2019, 2018 and 2017, (Gain) loss on asset disposals, net included charges of $19 million, $10 million and $17 million, respectively, related to disposals of assets, trade-ins of older assets for replacement assets and other retirements of assets from service in the normal course of business.