Basis of Presentation	9 Months Ended
Basis of Presentation	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of Merck & Co., Inc. (Merck or the Company) have been prepared pursuant to the rules and regulations for reporting on Form 10-Q. Accordingly, certain information and disclosures required by accounting principles generally accepted in the United States (U.S.) (GAAP) for complete consolidated financial statements are not included herein. These interim statements should be read in conjunction with the audited financial statements and notes thereto included in Merck’s Form 10-K filed on February 25, 2021. The results of operations of any interim period are not necessarily indicative of the results of operations for the full year. In the Company’s opinion, all adjustments necessary for a fair statement of these interim statements have been included and are of a normal and recurring nature. Reclassifications — Certain reclassifications have been made to prior year amounts to conform to the current year presentation. Spin-Off of Organon & Co. On June 2, 2021, Merck completed the spin-off of products from its women’s health, biosimilars and established brands businesses into a new, independent, publicly traded company named Organon & Co. (Organon) through a distribution of Organon’s publicly traded stock to Company shareholders. The established brands included in the transaction consisted of dermatology, non-opioid pain management, respiratory, select cardiovascular products, as well as the rest of Merck’s diversified brands franchise. Merck’s existing research pipeline programs continue to be owned and developed within Merck as planned. The historical results of the women’s health, biosimilars and established brands businesses that were contributed to Organon in the spin-off have been reflected as discontinued operations in the Company’s consolidated financial statements through the date of the spin-off (see Note 2). Recently Adopted Accounting Standards In December 2019, the Financial Accounting Standards Board (FASB) issued amended guidance on the accounting and reporting of income taxes. The guidance is intended to simplify the accounting for income taxes by removing exceptions related to certain intraperiod tax allocations and deferred tax liabilities, clarifying guidance primarily related to evaluating the step-up tax basis for goodwill in a business combination, and reflecting enacted changes in tax laws or rates in the annual effective tax rate. The Company adopted the new guidance effective January 1, 2021. There was no impact to the Company’s consolidated financial statements upon adoption. In January 2020, the FASB issued new guidance intended to clarify certain interactions between accounting standards related to equity securities, equity method investments and certain derivatives. The guidance addresses accounting for the transition into and out of the equity method of accounting and measuring certain purchased options and forward contracts to acquire investments. The Company adopted the new guidance effective January 1, 2021. There was no impact to the Company’s consolidated financial statements upon adoption. Recently Issued Accounting Standards Not Yet Adopted In March 2020, the FASB issued optional guidance to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting and subsequently issued clarifying amendments. The guidance provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions that reference the London Interbank Offered Rate (LIBOR) or another reference rate expected to be discontinued because of reference rate reform. The optional guidance is effective upon issuance and can be applied on a prospective basis at any time between January 1, 2020 through December 31, 2022. The Company is currently evaluating the impact of adoption on its consolidated financial statements. In August 2020, the FASB issued amended guidance on the accounting for convertible instruments and contracts in an entity’s own equity. The guidance removes the separation model for convertible debt instruments and preferred stock, amends requirements for conversion options to be classified in equity as well as amends diluted earnings per share (EPS) calculations for certain convertible debt instruments. The amended guidance is effective for interim and annual periods in 2022. Early adoption is permitted. The application of the amendments in the new guidance are to be applied either on a modified retrospective or a retrospective basis. The Company is currently evaluating the impact of adoption on its consolidated financial statements. In October 2021, the FASB issued amended guidance that requires acquiring entities to recognize and measure contract assets and liabilities in a business combination in accordance with existing revenue recognition guidance. The amended guidance is effective for interim and annual periods in 2023 and is to be applied prospectively. Early adoption is permitted on a retrospective basis to the beginning of the fiscal year of adoption. The Company is currently evaluating the impact of adoption on its consolidated financial statements.