Operating Activities Cash flow from operating activities represents the cash receipts and disbursements from all of our activities other than investing and financing activities. Operating cash flow is derived by adjusting net earnings for noncontrolling interest, non-cash operating items, gains and losses attributed to investing and financing activities and changes in operating assets and liabilities resulting from timing differences between the receipts and payments of cash and when the transactions are recognized in our results of operations. As a result, changes in cash from operating activities reflect the timing of cash collections from customers and alliance partners; payments to suppliers, alliance partners and employees; customer discounts and rebates; and tax payments in the ordinary course of business. For example, annual employee bonuses are typically paid in the first quarter of the subsequent year. In addition, cash collections continue to be impacted by longer payment terms for certain biologic products in the U.S., primarily our newer oncology products including  Opdivo ,  Yervoy  and  Empliciti  (90 days in 2019 and 90 to 120 days in 2018). The longer payment terms are used to more closely align with the insurance reimbursement timing for physicians and cancer centers following administration to the patients. The $2.1 billion change in cash flow from operating activities compared to 2018 was primarily attributable to: • Lower R&D licensing and collaboration payments of approximately $1.0 billion primarily due to the Nektar transaction in 2018. Partially offset by: Cash requirements from investing activities include cash used for acquisitions, manufacturing and facility-related capital expenditures and purchases of marketable securities with original maturities greater than 90 days at the time of purchase reduced by proceeds from business divestitures (including royalties) and the sale and maturity of marketable securities. The $8.9 billion change in cash flow from investing activities compared to 2018 was primarily attributable to higher net acquisition and other payments of approximately $23.4 billion primarily due to the acquisition of Celgene, partially offset by higher business divestiture proceeds of approximately $14.6 billion primarily due to the divestitures of  Otezla*  and UPSA consumer health business. Cash requirements from financing activities include cash used to pay dividends, repurchase common stock and repay long-term debt and other borrowings reduced by proceeds from the exercise of stock options and issuance of long-term debt and other borrowings. The $11.2 billion change in cash flow from financing activities compared to 2018 was primarily attributable to higher net borrowing activity of approximately $18.2 billion primarily resulting from the issuance of new notes in connection with the acquisition of Celgene, partially offset by accelerated stock repurchase cash payment of $7.0 billion. Payments due by period for our contractual obligations at December 31, 2019 were as follows: (a) Includes estimated future interest payments and periodic cash settlements of derivatives. (b) Includes only short-term uncertain tax benefits because of uncertainties regarding the timing of resolution. (c) Excludes other non-current liabilities because of uncertainties regarding the timing of resolution. 47 Contractual Obligations and Off-Balance Sheet Arrangements Financing Activities Investing Activities • Higher cash collections and timing of payments in the ordinary course of business of approximately $3.0 billion, including approximately $1.0 billion relating to Celgene; and • Higher income tax payments of approximately $750 million; and • Celgene acquisition and integration related payments of approximately $1.1 billion. Obligations Expiring by Period Dollars in Millions Total 2020 2021 2022 2023 2024 Later Years Short-term borrowings $ 583 $ 583 $ — $ — $ — $ — $ — Long-term debt 44,335 2,750 2,000 4,750 3,267 4,286 27,282 Interest on long-term debt (a) 21,659 1,627 1,483 1,428 1,292 1,191 14,638 Operating leases 966 165 145 130 104 68 354 Purchase obligations 3,353 1,143 717 526 384 262 321 Uncertain tax positions (b) 85 85 — — — — — Deemed repatriation transition tax 3,416 119 339 339 567 798 1,254 Total (c) $ 74,397 $ 6,472 $ 4,684 $ 7,173 $ 5,614 $ 6,605 $ 43,849