COMMITMENTS AND CONTINGENCIES Commitments We have entered into non-cancellable operating, capital, and finance leases for equipment and office, fulfillment, sortation, delivery, data center, physical store, and renewable energy facilities. Rental expense under operating lease agreements was $553 million and $859 million for Q3 2017 and Q3 2018 , and $1.4 billion and $2.5 billion for the nine months ended September 30, 2017 and 2018 . The following summarizes our principal contractual commitments, excluding open orders for purchases that support normal operations and are generally cancellable, as of September 30, 2018 (in millions): Three Months Ended December 31, Year Ended December 31, 2018 2019 2020 2021 2022 Thereafter Total Debt principal and interest $ 213 $ 2,186 $ 2,111 $ 1,833 $ 2,049 $ 31,769 $ 40,161 Capital lease obligations, including interest (1) 1,363 6,912 4,753 1,740 583 773 16,124 Finance lease obligations, including interest (2) 145 609 625 636 647 5,654 8,316 Operating leases 748 2,902 2,752 2,468 2,200 13,453 24,523 Unconditional purchase obligations (3) 137 3,760 3,488 3,265 3,054 8,096 21,800 Other commitments (4) (5) 841 1,734 1,157 1,184 649 7,936 13,501 Total commitments $ 3,447 $ 18,103 $ 14,886 $ 11,126 $ 9,182 $ 67,681 $ 124,425 ___________________ (1) Excluding interest, current capital lease obligations of $5.8 billion and $6.9 billion are recorded within Accrued expenses and other as of December 31, 2017 and September 30, 2018 , and $8.4 billion and $8.7 billion are recorded within Other long-term liabilities as of December 31, 2017 and September 30, 2018 . (2) Excluding interest, current finance lease obligations of $282 million and $391 million are recorded within Accrued expenses and other as of December 31, 2017 and September 30, 2018 , and $4.7 billion and $6.5 billion are recorded within Other long-term liabilities as of December 31, 2017 and September 30, 2018 . (3) Includes unconditional purchase obligations related to certain products offered in our Whole Foods Market stores and long-term agreements to acquire and license digital media content that are not reflected on the consolidated balance sheets. For those digital media content agreements with variable terms, we do not estimate the total obligation beyond any minimum quantities and/or pricing as of the reporting date. Purchase obligations associated with renewal provisions solely at the option of the content provider are included to the extent such commitments are fixed or a minimum amount is specified. (4) Includes the estimated timing and amounts of payments for rent and tenant improvements associated with build-to-suit lease arrangements and equipment lease arrangements that have not been placed in service and digital media content liabilities associated with long-term digital media content assets with initial terms greater than one year. (5) Excludes approximately $3.4 billion of accrued tax contingencies for which we cannot make a reasonably reliable estimate of the amount and period of payment, if any. Pledged Assets As of December 31, 2017 and September 30, 2018 , we have pledged or otherwise restricted $1.4 billion and $688 million of our cash, cash equivalents, and marketable securities, and certain property and equipment as collateral for real estate leases, amounts due to third-party sellers in certain jurisdictions, debt, and standby and trade letters of credit. Other Contingencies In 2016, we determined that we processed and delivered orders of consumer products for certain individuals and entities located outside Iran covered by the Iran Threat Reduction and Syria Human Rights Act or other United States sanctions and export control laws. The consumer products included books, music, other media, apparel, home and kitchen, health and beauty, jewelry, office, consumer electronics, software, lawn and patio, grocery, and automotive products. Our review is ongoing and we have voluntarily reported these orders to the United States Treasury Departments Office of Foreign Assets Control and the United States Department of Commerces Bureau of Industry and Security. We intend to cooperate fully with OFAC and BIS with respect to their review, which may result in the imposition of penalties. For additional information, see Item 5 of Part II, Other Information  Disclosure Pursuant to Section 13(r) of the Exchange Act. We are subject to claims related to various indirect taxes (such as sales, value added, consumption, service, and similar taxes), including in jurisdictions in which we already collect and remit such taxes. If the relevant taxing authorities were successfully to pursue these claims, we could be subject to significant additional tax liabilities. For example, in June 2017, the State of South Carolina issued an assessment for uncollected sales and use taxes for the period from January 2016 to March 2016, including interest and penalties. South Carolina is alleging that we should have collected sales and use taxes on transactions by our third-party sellers. We believe the assessment is without merit. If South Carolina or other states were successfully to seek additional adjustments of a similar nature, we could be subject to significant additional tax liabilities. We intend to defend ourselves vigorously in this matter. Legal Proceedings The Company is involved from time to time in claims, proceedings, and litigation, including the matters described in Item 8 of Part II, Financial Statements and Supplementary Data  Note 7  Commitments and Contingencies  Legal Proceedings of our 2017 Annual Report on Form 10-K and in Item 1 of Part I, Financial Statements  Note 3  Commitments and Contingencies  Legal Proceedings of our Quarterly Reports on Form 10-Q for the periods ended March 31, 2018 and June 30, 2018. The outcomes of our legal proceedings and other contingencies are inherently unpredictable, subject to significant uncertainties, and could be material to our operating results and cash flows for a particular period. In addition, for the matters we disclose that do not include an estimate of the amount of loss or range of losses, such an estimate is not possible or is immaterial, and we may be unable to estimate the possible loss or range of losses that could potentially result from the application of non-monetary remedies. See also Note 7  Income Taxes.