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Segment Reporting - Reconciliation of Segment Profits to Income Before Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Interest income	$ 343	$ 385	$ 328
Interest expense	(772)	(754)	(693)
Depreciation and amortization	(4,519)	(4,676)	(5,471)
Research and development	(9,752)	(10,339)	(10,261)
Restructuring costs	(632)	(776)	(651)
Loss on extinguishment of debt		(191)
Charge related to the settlement of worldwide Keytruda patent litigation	0	0	(625)
Income Before Taxes	8,701	6,521	4,659
Total segment profits
Segment Reporting Information [Line Items]
Depreciation and amortization	(335)	(212)	(183)
Income Before Taxes	26,054	24,322	23,644
Total segment profits | Pharmaceutical segment
Segment Reporting Information [Line Items]
Depreciation and amortization	(243)	(125)	(160)
Income Before Taxes	24,292	22,495	22,141
Total segment profits | Animal Health
Segment Reporting Information [Line Items]
Depreciation and amortization	(82)	(75)	(10)
Income Before Taxes	1,659	1,552	1,357
Total segment profits | Other segments
Segment Reporting Information [Line Items]
Depreciation and amortization	(10)	(12)	(13)
Income Before Taxes	103	275	146
Other profits
Segment Reporting Information [Line Items]
Income Before Taxes	6	26	481
Unallocated
Segment Reporting Information [Line Items]
Interest income	343	385	328
Interest expense	(772)	(754)	(693)
Depreciation and amortization	(1,334)	(1,378)	(1,585)
Research and development	(8,853)	(9,481)	(9,218)
Amortization of purchase accounting adjustments	(2,664)	(3,056)	(3,692)
Restructuring costs	(632)	(776)	(651)
Charge related to termination of collaboration agreement with Samsung	(423)	0	0
Loss on extinguishment of debt	0	(191)	0
Gain on sale of certain migraine clinical development programs	0	0	100
Charge related to the settlement of worldwide Keytruda patent litigation	0	0	(625)
Other unallocated, net	$ (3,024)	$ (2,576)	$ (3,430)

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