Property



	Estimated Useful Lives in Years	December 31, 2017			December 31, 2016
Land		$	1,647		$	1,587
Buildings and improvements	5-40	7,471			6,217
Machinery and equipment	3-27	23,915			21,613
Special tools	1-13	21,113			19,359
Construction in progress		6,188			4,493
Total property		60,334			53,269
Less: accumulated depreciation		(24,081		)	(20,666		)
Total property, net		$	36,253		$	32,603

The amount of capitalized software included in Property, net was $1.2 billion and $1.1 billion at December 31, 2017 and 2016. The amount of interest capitalized and excluded from Automotive interest expense related to Property, net was insignificant in the years ended December 31, 2017, 2016 and 2015.



	Years Ended December 31,
	2017		2016		2015
Depreciation and amortization expense	$	4,966	$	4,622	$	3,904
Impairment charges	$	199	$	68	$	628
Capitalized software amortization expense(a)	$	459	$	458	$	374

__________


(a)	Included in depreciation and amortization expense.