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, 2016 and 2015 were as follows:

December 31,	Useful Lives (Years)	2016		2015
(Dollars in millions)
Land	N/A	$	35	$	36
Buildings	20		297		295
Leasehold and land improvements	1-30		1,153		1,103
Cell site equipment	7-25		3,383		3,383
Switching equipment	5-8		976		960
Office furniture and equipment	3-5		420		502
Other operating assets and equipment	3-5		53		79
System development	1-7		1,217		1,169
Work in process	N/A		178		142
Total property, plant and equipment, gross			7,712		7,669
Accumulated depreciation and amortization			(5,242)		(5,020)
Total property, plant and equipment, net		$	2,470	$	2,649

Depreciation and amortization expense totaled $607 million, $596 million and $593 million in 2016, 2015 and 2014, respectively. In 2016, 2015 and 2014, (Gain) loss on asset disposals, net included charges of $22 million, $16 million and $21 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.