Taxes on Income	3 Months Ended
Mar. 31, 2021
Income Tax Disclosure [Abstract]
Taxes on Income	Taxes on IncomeThe effective income tax rates of 8.0% and 16.1% for the first quarter of 2021 and 2020, respectively, reflect the impacts of acquisition and divestiture-related costs and restructuring costs, partially offset by the beneficial impact of foreign earnings. In the first quarter of 2021, the Internal Revenue Service (IRS) concluded its examinations of Merck’s 2015-2016 U.S. federal income tax returns. As a result, the Company was required to make a payment of $190 million. The Company’s reserves for unrecognized tax benefits for the years under examination exceeded the adjustments relating to this examination period and therefore the Company recorded a $237 million net tax benefit in the first quarter of 2021. This net benefit reflects reductions in reserves for unrecognized tax benefits and other related liabilities for tax positions relating to the years that were under examination.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

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