Our property, plant and equipment, net, consisted of the following (in millions):


	June 30,			December 31,
	2021			2020
Machinery, equipment, vehicles and office furniture	$	9,156		$	8,493
Tooling		2,038			1,811
Leasehold improvements		1,596			1,421
Land and buildings		3,725			3,662
Computer equipment, hardware and software		1,148			856
Construction in progress		3,826			1,621
		21,489			17,864
Less: Accumulated depreciation		(5,824	)		(5,117	)
Total	$	15,665		$	12,747

Construction in progress is primarily comprised of construction of Gigafactory Berlin and Gigafactory Texas, expansion of Gigafactory Shanghai and equipment and tooling related to the manufacturing of our products. We are currently constructing Gigafactory Berlin under conditional permits in anticipation of being granted final permits. Completed assets are transferred to their respective asset classes, and depreciation begins when an asset is ready for its intended use. Interest on outstanding debt is capitalized during periods of significant capital asset construction and amortized over the useful lives of the related assets. During the three and six months ended June 30, 2021, we capitalized $23 million and $38 million, respectively, of interest. During the three and six months ended June 30, 2020, we capitalized $10 million and $20 million, respectively, of interest.

Depreciation expense during the three and six months ended June 30, 2021 was $461 million and $885 million, respectively. Depreciation expense during the three and six months ended June 30, 2020 was $356 million and $727 million, respectively. Gross property, plant and equipment under finance leases as of June 30, 2021 and December 31, 2020 was $2.43 billion and $2.28 billion, respectively, with accumulated depreciation of $1.01 billion and $816 million, respectively.

Panasonic has partnered with us on Gigafactory Nevada with investments in the production equipment that it uses to manufacture and supply us with battery cells. Under our arrangement with Panasonic, we plan to purchase the full output from their production equipment at negotiated prices. As the terms of the arrangement convey a finance lease under ASC 842, Leases, we account for their production equipment as leased assets when production commences. We account for each lease and any non-lease components associated with that lease as a single lease component for all asset classes, except production equipment classes embedded in supply agreements. This results in us recording the cost of their production equipment within Property, plant and equipment, net, on the consolidated balance sheets with a corresponding liability recorded to debt and finance leases. Depreciation on Panasonic production equipment is computed using the units-of-production method whereby capitalized costs are amortized over the total estimated productive life of the respective assets. As of June 30, 2021 and December 31, 2020, we had cumulatively capitalized costs of $1.79 billion and $1.77 billion, respectively, on the consolidated balance sheets in relation to the production equipment under our Panasonic arrangement.