LEASES

We lease our offices and other property through operating leases. Rental expense is charged to operations as incurred. For 2017, 2016 and 2015, total rental expense for operating leases was $16 million, $17 million and $16 million, respectively. At December 31, 2017, minimum payments for operating leases having initial non-cancelable terms in excess of one year were as follows:



(Millions of dollars)
2018	$	8
2019	6
2020	4
2021	3
2022	3
Thereafter	3
Total	$	27

We had a commitment to purchase the corporate headquarters building for $91 million as of December 31, 2017. The building purchase was closed on January 4, 2018.