Property, Plant and Equipment

12 Months Ended

Dec. 31, 2019

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)	2019		2018
Land and land improvements	⁽¹⁾	$	15.3	$	15.6
Buildings and building improvements	15-30	115.8		122.2
Machinery, tools and equipment	5-12	99.3		99.6
Leasehold improvements ⁽²⁾	10	25.5		26.9
Computer equipment	3	148.7		174.5
Computer software	5-10	143.5		142.9
Furniture and fixtures	5-8	67.6		70.3
Tooling	3-5	137.7		140.9
Construction in progress		5.0		5.3
Total property plant and equipment, at cost		$	758.4	$	798.2
Less accumulated depreciation and amortization		526.9		494.1
Total property plant and equipment, net		$	231.5	$	304.1


⁽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 2019, 2018 and 2017, depreciation expense, computed on a straight-line basis over the estimated useful lives of the related assets, was $82.2, $94.4 and $92.9, respectively.