CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Statement of Comprehensive Income [Abstract]
Net (Loss) Income Attributable to Merck & Co., Inc.	$ (4,240)	$ 5,079
Other Comprehensive Income (Loss) Net of Taxes:
Net unrealized gain (loss) on derivatives, net of reclassifications	216	(217)
Benefit plan net gain (loss) and prior service credit (cost), net of amortization	5	(18)
Cumulative translation adjustment	6	215
Other comprehensive income (loss), net of taxes	227	(20)
Comprehensive (Loss) Income Attributable to Merck & Co., Inc.	$ (4,013)	$ 5,059