Property and Equipment

12 Months Ended

Dec. 31, 2015

Property, Plant and Equipment [Abstract]

Property and equipment consists of the following (in millions):



	December 31,
	2015			2014
Land	$	596		$	153
Buildings	2,273			1,420
Leasehold improvements	447			304
Network equipment	3,633			3,020
Computer software, office equipment and other	248			149
Construction in progress	622			738
Total	7,819			5,784
Less: Accumulated depreciation	(2,132		)	(1,817		)
Property and equipment, net	$	5,687		$	3,967

Depreciation expense on property and equipment was $1.22 billion, $923 million, and $857 million during 2015, 2014, and 2013, respectively.

Property and equipment at December 31, 2015 and 2014 includes $287 million and $700 million, respectively, acquired under capital lease agreements, of which the majority is included in network equipment. Accumulated depreciation of property and equipment acquired under these capital leases was $71 million and $425 million at December 31, 2015 and 2014, respectively.

Construction in progress includes costs primarily related to construction of data centers and office buildings, and network equipment infrastructure to support our data centers around the world. The construction of office buildings includes the leased office space in London, United Kingdom for which we are considered to be the owner for accounting purposes. See Note 10 in these notes to the consolidated financial statements for additional information. No interest was capitalized during the years ended December 31, 2015 and 2014. Interest capitalized during the year ended December 31, 2013 was not material.