We lease substantially all of our hotels to a wholly owned subsidiary that qualifies as a taxable REIT subsidiary due to federal income tax restrictions on a REIT’s ability to derive revenue directly from the operation and management of a hotel.

As of December 31, 2018, all or a portion of 25 of our hotels are subject to ground leases, generally with multiple renewal options, all of which are accounted for as operating leases. For lease agreements with scheduled rent increases, we recognize the fixed portion of the lease expense ratably over the term of the lease. Certain of these leases contain provisions for the payment of contingent rentals based on a percentage of sales in excess of stipulated amounts.

We also have leases on facilities used in our former restaurant business, all of which we subsequently subleased. These leases and subleases contain one or more renewal options, generally for five- or ten-year periods. The restaurant leases are accounted for as operating leases. Our contingent liability related to these leases is $7 million as of December 31, 2018. We, however, consider the likelihood of any material funding related to these leases to be remote. Our leasing activity also includes those entered into by our hotels for various types of equipment, such as computer equipment, vehicles and telephone systems. Equipment leases are accounted for either as operating or capital leases, depending upon the characteristics of the particular lease arrangement. Equipment leases that are characterized as capital leases are classified as furniture and equipment and are depreciated over the life of the lease. The amortization expense applicable to capitalized leases is included in depreciation expense.

The following table presents the future minimum annual rental commitments required under non-cancelable operating leases for which we are the lessee (in millions):

	As of December 31, 2018
2019	$	46
2020		44
2021		43
2022		40
2023		37
Thereafter		1,309
Total minimum lease payments	$	1,519

Minimum payments for the operating leases have not been reduced by aggregate minimum sublease rentals from restaurants of approximately $6 million that are payable to us under non-cancelable subleases.

Rent expense is included in other property-level expenses and consists of (in millions):

	Year ended December 31,
	2018			2017			2016
Minimum rentals on operating leases	$	45		$	46		$	45
Additional rentals based on sales		38			38			38
Less: sublease rentals		(1	)		(1	)		(2	)
	$	82		$	83		$	81