ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2022
Accounting Policies [Abstract]
Basis of Presentation	The accompanying Condensed Consolidated Financial Statements and related Notes to Condensed Consolidated Financial Statements of Gilead Sciences, Inc. (“Gilead,” “we,” “our” or “us”) should be read in conjunction with the audited Consolidated Financial Statements and the related notes thereto for the year ended December 31, 2021, included in our Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission. There have been no material changes to our organization or summary of significant accounting policies as disclosed in that filing except for our classification of expenses related to development milestones and other collaboration payments made prior to regulatory approval of a developed product. Beginning in the second quarter of 2022, we reclassified such expenses from Research and development expenses to Acquired in-process research and development expenses in the Condensed Consolidated Statements of Income. Concurrently, we reclassified the cash payments related to these expenses from Other to Acquisitions, including in-process research and development, net of cash acquired within Investing Activities in the Condensed Consolidated Statements of Cash Flows. We believe this presentation assists users of the financial statements to better understand the total costs incurred to acquire in-process research and development (“IPR&D”) projects. Prior periods have been revised to reflect this classification, resulting in a reduction of previously-reported Research and development expenses of $46 million and $93 million for the three and nine months ended September 30, 2021, respectively, and $8 million for the three months ended March 31, 2022. These interim financial statements have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information and include all adjustments consisting of normal recurring adjustments that the management of Gilead believes are necessary for a fair presentation of the periods presented and are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period. Certain amounts and percentages in these Condensed Consolidated Financial Statements and accompanying notes may not sum or recalculate due to rounding.
Fair Value Measurements	We determine the fair value of financial and non-financial assets and liabilities using the fair value hierarchy, which establishes three levels of inputs that may be used to measure fair value, as follows: •Level 1 inputs include quoted prices in active markets for identical assets or liabilities; •Level 2 inputs include observable inputs other than Level 1 inputs, such as quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability; and •Level 3 inputs include unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the underlying asset or liability. Our Level 3 assets and liabilities include those whose fair value measurements are determined using pricing models, discounted cash flow methodologies or similar valuation techniques and significant management judgment or estimation. Our financial instruments consist primarily of cash and cash equivalents, marketable debt securities, accounts receivable, foreign currency exchange contracts, equity securities, accounts payable and short-term and long-term debt. Cash and cash equivalents, marketable debt securities, certain equity securities and foreign currency exchange contracts are reported at their respective fair values on our Condensed Consolidated Balance Sheets. Equity securities without readily determinable fair values are recorded using the measurement alternative of cost less impairment, if any, adjusted for observable price changes in orderly transactions for identical or similar investments of the same issuer. Short-term and long-term debt are reported at their amortized costs on our Condensed Consolidated Balance Sheets. The remaining financial instruments are reported on our Condensed Consolidated Balance Sheets at amounts that approximate current fair values. Level 2 Inputs Available-for-Sale Debt Securities For our available-for-sale debt securities, we estimate the fair values by reviewing trading activity and pricing as of the measurement date, and taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income-based and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate the fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data and other observable inputs. Foreign Currency Derivative Contracts Substantially all of our foreign currency derivative contracts have maturities within an 18-month time horizon and all are with counterparties that have a minimum credit rating of A- or equivalent by S&P Global Ratings, Moody’s Investors Service, Inc. or Fitch Ratings, Inc. We estimate the fair values of these contracts by taking into consideration the valuations obtained from a third-party valuation service that utilizes an income-based industry standard valuation model for which all significant inputs are observable, either directly or indirectly. These inputs include foreign currency exchange rates, Secured Overnight Financing Rate and swap rates. These inputs, where applicable, are observable at commonly quoted intervals. Level 3 Inputs Contingent Consideration In connection with our first quarter 2021 acquisition of MYR, we recorded a liability for contingent consideration, which is revalued each reporting period until the related contingency is resolved. The contingent consideration was estimated using probability-weighted scenarios for U.S. Food and Drug Administration (“FDA”) approval of Hepcludex.