Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information. The financial statements include all adjustments consisting of normal recurring adjustments that the management of Gilead Sciences, Inc. (Gilead, we, our or us) believes are necessary for a fair presentation of the periods presented. These interim financial results are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period. The accompanying Condensed Consolidated Financial Statements include the accounts of Gilead, our wholly-owned subsidiaries and certain variable interest entities for which we are the primary beneficiary. All intercompany transactions have been eliminated. For consolidated entities where we own or are exposed to less than 100% of the economics, we record net income (loss) attributable to noncontrolling interest in our Condensed Consolidated Statements of Operations equal to the percentage of the economic or ownership interest retained in such entities by the respective noncontrolling parties. For investments in entities over which we have significant influence but do not meet the requirements for consolidation and have not elected the fair value option, we use the equity method of accounting with our share of the underlying income or loss of such entities reported in Other income (expense), net on our Condensed Consolidated Statements of Operations. We have elected the fair value option to account for our equity investment in Galapagos NV (Galapagos) over which we have significant influence. See Note 6. Collaborative and Other Arrangements for additional information. We assess whether we are the primary beneficiary of a variable interest entity (VIE) at the inception of the arrangement and at each reporting date. This assessment is based on our power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and our obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. As of September 30, 2019, we did not have any material VIEs. The accompanying Condensed Consolidated Financial Statements and related Notes to Condensed Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements and the related notes thereto for the year ended December 31, 2018, included in our Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission. Significant Accounting Policies, Estimates and Judgments The preparation of these Condensed Consolidated Financial Statements requires us to make estimates and judgments that affect the reported amounts of assets, liabilities, revenues and expenses and related disclosures. On an ongoing basis, we evaluate our significant accounting policies and estimates. We base our estimates on historical experience and on various market-specific and other relevant assumptions that we believe to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Estimates are assessed each period and updated to reflect current information. Actual results may differ significantly from these estimates. Reclassifications Up-front and milestone payments related to collaborative and other arrangements were classified as cash flows from investing activities in the Condensed Consolidated Statements of Cash Flows for the nine months ended September 30, 2019 to provide better alignment between the cash flows and the underlying nature of the transactions. Payments of $254 million for the six months ended June 30, 2019 were reclassified from operating activities to investing activities in the Condensed Consolidated Statements of Cash Flows. Comparative prior year amounts were not material and were not reclassified. Concentrations of Risk We are subject to credit risk from our portfolio of cash equivalents and marketable securities. Under our investment policy, we limit amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. We are not exposed to any significant concentrations of credit risk from these financial instruments. The goals of our investment policy, in order of priority, are as follows: safety and preservation of principal and diversification of risk; liquidity of investments sufficient to meet cash flow requirements; and a competitive after-tax rate of return. We are also subject to credit risk from our accounts receivable related to our product sales. The majority of our trade accounts receivable arises from product sales in the United States and Europe. To date, we have not experienced significant losses with respect to the collection of our accounts receivable. We believe that our allowance for doubtful accounts was adequate as of September 30, 2019. Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update No. 2016-02 “Leases” (ASU 2016-02) and subsequently issued supplemental adoption guidance and clarification (collectively, Topic 842). Topic 842 amends a number of aspects of lease accounting, including requiring lessees to recognize right-of-use assets and lease liabilities for operating leases with a lease term greater than one year. Topic 842 supersedes Topic 840 “Leases.” On January 1, 2019, we adopted Topic 842 using the modified retrospective approach. Results for reporting periods beginning after January 1, 2019 are presented under Topic 842, while prior period amounts are not adjusted and continue to be reported in accordance with our historical accounting under Topic 840. We elected the package of practical expedients permitted under the transition guidance within Topic 842, which allowed us to carry forward the historical lease classification, retain the initial direct costs for any leases that existed prior to the adoption of the standard and not reassess whether any contracts entered into prior to the adoption are leases. We also elected to account for lease and nonlease components in our lease agreements as a single lease component in determining lease assets and liabilities. In addition, we elected not to recognize the right-of-use assets and liabilities for leases with lease terms of one year or less. Upon adoption of Topic 842, we recorded $441 million of right-of-use assets within Other long-term assets and $490 million of operating lease liabilities, classified primarily within Other long-term obligations on our Condensed Consolidated Balance Sheet, as of January 1, 2019. The adoption did not have a material impact on our Condensed Consolidated Statements of Operations or Condensed Consolidated Statements of Cash Flows. See Note 10. Leases for additional information. Recently Issued Accounting Standards Not Yet Adopted In June 2016, the FASB issued Accounting Standards Update No. 2016-13 “Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments” (ASU 2016-13). ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets. In April 2019, the FASB issued clarification to ASU 2016-13 within ASU 2019-04 “Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments.” The guidance will become effective for us beginning in the first quarter of 2020 and must be adopted using a modified retrospective approach, with certain exceptions. We do not expect the adoption of these standards to have a material impact on our Condensed Consolidated Financial Statements. In November 2018, the FASB issued Accounting Standards Update No. 2018-18 “Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606” (ASU 2018-18). ASU 2018-18 clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, the update precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue if the counterparty is not a customer for that transaction. This guidance will become effective for us beginning in the first quarter of 2020 and will be applied retrospectively to January 1, 2018 when we initially adopted Topic 606. Early adoption is permitted. We do not expect the adoption of this standard to have a material impact on our Condensed Consolidated Financial Statements.

The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information. The financial statements include all adjustments consisting of normal recurring adjustments that the management of Gilead Sciences, Inc. (Gilead, we, our or us) believes are necessary for a fair presentation of the periods presented. These interim financial results are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period.

The accompanying Condensed Consolidated Financial Statements include the accounts of Gilead, our wholly-owned subsidiaries and certain variable interest entities for which we are the primary beneficiary. All intercompany transactions have been eliminated. For consolidated entities where we own or are exposed to less than 100% of the economics, we record net income (loss) attributable to noncontrolling interest in our Condensed Consolidated Statements of Operations equal to the percentage of the economic or ownership interest retained in such entities by the respective noncontrolling parties.

For investments in entities over which we have significant influence but do not meet the requirements for consolidation and have not elected the fair value option, we use the equity method of accounting with our share of the underlying income or loss of such entities reported in Other income (expense), net on our Condensed Consolidated Statements of Operations. We have elected the fair value option to account for our equity investment in Galapagos NV (Galapagos) over which we have significant influence. See Note 6. Collaborative and Other Arrangements for additional information.

We assess whether we are the primary beneficiary of a variable interest entity (VIE) at the inception of the arrangement and at each reporting date. This assessment is based on our power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and our obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. As of September 30, 2019, we did not have any material VIEs.

The accompanying Condensed Consolidated Financial Statements and related Notes to Condensed Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements and the related notes thereto for the year ended December 31, 2018, included in our Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission.

The preparation of these Condensed Consolidated Financial Statements requires us to make estimates and judgments that affect the reported amounts of assets, liabilities, revenues and expenses and related disclosures. On an ongoing basis, we evaluate our significant accounting policies and estimates. We base our estimates on historical experience and on various market-specific and other relevant assumptions that we believe to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Estimates are assessed each period and updated to reflect current information. Actual results may differ significantly from these estimates.

Up-front and milestone payments related to collaborative and other arrangements were classified as cash flows from investing activities in the Condensed Consolidated Statements of Cash Flows for the nine months ended September 30, 2019 to provide better alignment between the cash flows and the underlying nature of the transactions. Payments of $254 million for the six months ended June 30, 2019 were reclassified from operating activities to investing activities in the Condensed Consolidated Statements of Cash Flows. Comparative prior year amounts were not material and were not reclassified.

We are subject to credit risk from our portfolio of cash equivalents and marketable securities. Under our investment policy, we limit amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. We are not exposed to any significant concentrations of credit risk from these financial instruments. The goals of our investment policy, in order of priority, are as follows: safety and preservation of principal and diversification of risk; liquidity of investments sufficient to meet cash flow requirements; and a competitive after-tax rate of return.

We are also subject to credit risk from our accounts receivable related to our product sales. The majority of our trade accounts receivable arises from product sales in the United States and Europe. To date, we have not experienced significant losses with respect to the collection of our accounts receivable. We believe that our allowance for doubtful accounts was adequate as of September 30, 2019.

In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update No. 2016-02 “Leases” (ASU 2016-02) and subsequently issued supplemental adoption guidance and clarification (collectively, Topic 842). Topic 842 amends a number of aspects of lease accounting, including requiring lessees to recognize right-of-use assets and lease liabilities for operating leases with a lease term greater than one year. Topic 842 supersedes Topic 840 “Leases.”

On January 1, 2019, we adopted Topic 842 using the modified retrospective approach. Results for reporting periods beginning after January 1, 2019 are presented under Topic 842, while prior period amounts are not adjusted and continue to be reported in accordance with our historical accounting under Topic 840. We elected the package of practical expedients permitted under the transition guidance within Topic 842, which allowed us to carry forward the historical lease classification, retain the initial direct costs for any leases that existed prior to the adoption of the standard and not reassess whether any contracts entered into prior to the adoption are leases. We also elected to account for lease and nonlease components in our lease agreements as a single lease component in determining lease assets and liabilities. In addition, we elected not to recognize the right-of-use assets and liabilities for leases with lease terms of one year or less.

Upon adoption of Topic 842, we recorded $441 million of right-of-use assets within Other long-term assets and $490 million of operating lease liabilities, classified primarily within Other long-term obligations on our Condensed Consolidated Balance Sheet, as of January 1, 2019. The adoption did not have a material impact on our Condensed Consolidated Statements of Operations or Condensed Consolidated Statements of Cash Flows. See Note 10. Leases for additional information.

In June 2016, the FASB issued Accounting Standards Update No. 2016-13 “Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments” (ASU 2016-13). ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets. In April 2019, the FASB issued clarification to ASU 2016-13 within ASU 2019-04 “Codification Improvements to Topic 326, Financial Instruments-Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments.” The guidance will become effective for us beginning in the first quarter of 2020 and must be adopted using a modified retrospective approach, with certain exceptions. We do not expect the adoption of these standards to have a material impact on our Condensed Consolidated Financial Statements.

In November 2018, the FASB issued Accounting Standards Update No. 2018-18 “Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606” (ASU 2018-18). ASU 2018-18 clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, the update precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue if the counterparty is not a customer for that transaction. This guidance will become effective for us beginning in the first quarter of 2020 and will be applied retrospectively to January 1, 2018 when we initially adopted Topic 606. Early adoption is permitted. We do not expect the adoption of this standard to have a material impact on our Condensed Consolidated Financial Statements.