Property, plant, and equipment were composed of the following:


	December 31
Millions of dollars	2021		2020
Land	$	120	$	120
Buildings and property improvements	1,608		1,652
Machinery, equipment, and other	14,040		13,592
Total	15,768		15,364
Less accumulated depreciation	11,442		11,039
Net property, plant, and equipment	$	4,326	$	4,325

During the year ended December 31, 2020, a $2.3 billion impairment charge was recorded related to property, plant, and equipment. See Note 2 to the consolidated financial statements for further discussion on impairments and other charges.

Classes of assets are depreciated over the following useful lives:


	Buildings and Property Improvements
	2021	2020
1 - 10 years	17%	13%
11 - 20 years	39%	41%
21 - 30 years	24%	21%
31 - 40 years	20%	25%


	Machinery, Equipment, and Other
	2021	2020
1 - 5 years	49%	49%
6 - 10 years	41%	41%
11 - 20 years	10%	10%