Commitments and Contingencies The Company leases facilities and equipment under long-term operating leases that are non-cancelable and expire on various dates. Rent expense under all operating leases for the years ended December 31, 2018 , 2017 and 2016 was $751 million , $710 million and $608 million , respectively. As of December 31, 2018 , future minimum annual lease payments, net of sublease income, under all non-cancelable operating leases were as follows: (in millions) Future Minimum Lease Payments 2019 $ 669 2020 592 2021 511 2022 423 2023 338 Thereafter 1,343 The Company provides guarantees related to its service level under certain contracts. If minimum standards are not met, the Company may be financially at risk up to a stated percentage of the contracted fee or a stated dollar amount. None of the amounts accrued, paid or charged to income for service level guarantees were material as of December 31, 2018 , 2017 or 2016 . As of December 31, 2018 , the Company had outstanding, undrawn letters of credit with financial institutions of $83 million and surety bonds outstanding with insurance companies of $1.3 billion , primarily to bond contractual performance. Pending Acquisition In December 2017, the Company entered into an agreement to acquire a company in the health care sector for a total of approximately $4.3 billion . Legal Matters Because of the nature of its businesses, the Company is frequently made party to a variety of legal actions and regulatory inquiries, including class actions and suits brought by members, care providers, consumer advocacy organizations, customers and regulators, relating to the Companys businesses, including management and administration of health benefit plans and other services. These matters include medical malpractice, employment, intellectual property, antitrust, privacy and contract claims and claims related to health care benefits coverage and other business practices. The Company records liabilities for its estimates of probable costs resulting from these matters where appropriate. Estimates of costs resulting from legal and regulatory matters involving the Company are inherently difficult to predict, particularly where the matters: involve indeterminate claims for monetary damages or may involve fines, penalties or punitive damages; present novel legal theories or represent a shift in regulatory policy; involve a large number of claimants or regulatory bodies; are in the early stages of the proceedings; or could result in a change in business practices. Accordingly, the Company is often unable to estimate the losses or ranges of losses for those matters where there is a reasonable possibility or it is probable that a loss may be incurred. Government Investigations, Audits and Reviews The Company has been involved or is currently involved in various governmental investigations, audits and reviews. These include routine, regular and special investigations, audits and reviews by CMS, state insurance and health and welfare departments, state attorneys general, the Office of the Inspector General, the Office of Personnel Management, the Office of Civil Rights, the Government Accountability Office, the Federal Trade Commission, U.S. Congressional committees, the U.S. Department of Justice, the SEC, the Internal Revenue Service, the U.S. Drug Enforcement Administration, the U.S. Department of Labor, the Federal Deposit Insurance Corporation, the Defense Contract Audit Agency and other governmental authorities. Similarly, our international businesses are also subject to investigations, audits and reviews by applicable foreign governments, including South American and other non-U.S. governmental authorities. Certain of the Companys businesses have been reviewed or are currently under review, including for, among other matters, compliance with coding and other requirements under the Medicare risk-adjustment model. CMS has selected certain of the Companys local plans for risk adjustment data validation (RADV) audits to validate the coding practices of and supporting documentation maintained by health care providers and such audits may result in retrospective adjustments to payments made to the Companys health plans. On February 14, 2017, the Department of Justice (DOJ) announced its decision to pursue certain claims within a lawsuit initially asserted against the Company and filed under seal by a whistleblower in 2011. The whistleblowers complaint, which was unsealed on February 15, 2017, alleges that the Company made improper risk adjustment submissions and violated the False Claims Act. On February 12, 2018, the court granted in part and denied in part the Companys motion to dismiss. In May 2018, DOJ moved to dismiss the Companys counterclaims, which were filed in March 2018, and moved for partial summary judgment. Those motions were argued in September 2018. The Company cannot reasonably estimate the outcome that may result from this matter given its procedural status.