Inventories and Equipment on Operating Leases, Net

The following is a summary of Inventories by major category:



	December 31,
	2018		2017
Finished goods	$	699	$	777
Work-in-process	49		49
Raw materials	70		89
Total Inventories	$	818	$	915

The transfer of equipment from our inventories to equipment subject to an operating lease is presented in our Consolidated Statements of Cash Flows in the operating activities section. Equipment on operating leases and similar arrangements consists of our equipment rented to customers and depreciated to estimated salvage value at the end of the lease term.

Equipment on operating leases and the related accumulated depreciation were as follows:



	December 31,
	2018			2017
Equipment on operating leases	$	1,519		$	1,546
Accumulated depreciation	(1,077		)	(1,092		)
Equipment on operating leases, net	$	442		$	454

Depreciable lives generally vary from three to four years consistent with our planned and historical usage of the equipment subject to operating leases. Our equipment operating lease terms vary, generally from one to three years. Estimated minimum future revenues associated with Equipment on operating leases are as follows:



2019		2020		2021		2022		2023		Thereafter
$	260	$	178	$	111	$	61	$	21	$	2

Total contingent rentals on operating leases, consisting principally of usage charges in excess of minimum contracted amounts, for the years ended December 31, 2018, 2017 and 2016 amounted to $120, $119 and $132, respectively.