Property, Plant and Equipment

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

The following is a summary of property, plant and equipment, at cost less accumulated depreciation and amortization as of December 31:



	Estimated Useful Life (years)	2018		2017
Land and land improvements	⁽¹⁾	$	15.6	$	16.0
Buildings and building improvements	15-30	122.2		112.9
Machinery, tools and equipment	5-12	99.6		108.2
Leasehold improvements ⁽²⁾	10	26.9		28.3
Computer equipment	3	174.5		153.8
Computer software	5-10	142.9		146.6
Furniture and fixtures	5-8	70.3		73.4
Tooling	3-5	140.9		136.4
Construction in progress		5.3		7.7
Total property plant and equipment, at cost		$	798.2	$	783.3
Less accumulated depreciation and amortization		494.1		418.8
Total property plant and equipment, net		$	304.1	$	364.5


⁽¹⁾	Estimated useful life for land and land improvements is perpetual and 15 years, respectively.


⁽²⁾	The estimated useful life for leasehold improvements is the lesser of 10 years or the term of the lease.

During 2018, 2017 and 2016, depreciation expense, computed on a straight-line basis over the estimated useful lives of the related assets, was $105.3, $92.9 and $61.8, respectively. The increase in computer equipment reflects the Company's investment in its IT infrastructure.