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Segment Reporting - Sales of Company's Products (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Sales	$ 12,080	$ 12,057
Operating Segments
Segment Reporting Information [Line Items]
Sales	12,093	11,892
Other
Segment Reporting Information [Line Items]
Sales	(13)	165
United States
Segment Reporting Information [Line Items]
Sales	5,136	5,137
United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	5,078	5,121
United States | Other
Segment Reporting Information [Line Items]
Sales	58	16
International
Segment Reporting Information [Line Items]
Sales	6,943	6,920
International | Operating Segments
Segment Reporting Information [Line Items]
Sales	7,015	6,771
International | Other
Segment Reporting Information [Line Items]
Sales	(72)	149
Total Pharmaceutical segment sales | Operating Segments
Segment Reporting Information [Line Items]
Sales	10,675	10,655
Total Pharmaceutical segment sales | Operating Segments | Keytruda
Segment Reporting Information [Line Items]
Sales	3,899	3,284
Total Pharmaceutical segment sales | Operating Segments | Alliance revenue - Lynparza (1)
Segment Reporting Information [Line Items]
Sales	228	145
Total Pharmaceutical segment sales | Operating Segments | Alliance revenue - Lenvima (1)
Segment Reporting Information [Line Items]
Sales	130	128
Total Pharmaceutical segment sales | Operating Segments | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	917	1,097
Total Pharmaceutical segment sales | Operating Segments | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	449	435
Total Pharmaceutical segment sales | Operating Segments | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	171	256
Total Pharmaceutical segment sales | Operating Segments | RotaTeq
Segment Reporting Information [Line Items]
Sales	158	222
Total Pharmaceutical segment sales | Operating Segments | Vaqta
Segment Reporting Information [Line Items]
Sales	34	60
Total Pharmaceutical segment sales | Operating Segments | Bridion
Segment Reporting Information [Line Items]
Sales	340	299
Total Pharmaceutical segment sales | Operating Segments | Prevymis
Segment Reporting Information [Line Items]
Sales	82	60
Total Pharmaceutical segment sales | Operating Segments | Noxafil
Segment Reporting Information [Line Items]
Sales	67	94
Total Pharmaceutical segment sales | Operating Segments | Primaxin
Segment Reporting Information [Line Items]
Sales	65	51
Total Pharmaceutical segment sales | Operating Segments | Cancidas
Segment Reporting Information [Line Items]
Sales	57	55
Total Pharmaceutical segment sales | Operating Segments | Invanz
Segment Reporting Information [Line Items]
Sales	57	64
Total Pharmaceutical segment sales | Operating Segments | Zerbaxa
Segment Reporting Information [Line Items]
Sales	(8)	37
Total Pharmaceutical segment sales | Operating Segments | Simponi
Segment Reporting Information [Line Items]
Sales	214	215
Total Pharmaceutical segment sales | Operating Segments | Remicade
Segment Reporting Information [Line Items]
Sales	85	88
Total Pharmaceutical segment sales | Operating Segments | Belsomra
Segment Reporting Information [Line Items]
Sales	79	79
Total Pharmaceutical segment sales | Operating Segments | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	209	245
Total Pharmaceutical segment sales | Operating Segments | Zetia
Segment Reporting Information [Line Items]
Sales	92	145
Total Pharmaceutical segment sales | Operating Segments | Vytorin
Segment Reporting Information [Line Items]
Sales	41	53
Total Pharmaceutical segment sales | Operating Segments | Atozet
Segment Reporting Information [Line Items]
Sales	112	122
Total Pharmaceutical segment sales | Operating Segments | Alliance revenue - Adempas (2)
Segment Reporting Information [Line Items]
Sales	74	53
Total Pharmaceutical segment sales | Operating Segments | Adempas
Segment Reporting Information [Line Items]
Sales	55	56
Total Pharmaceutical segment sales | Operating Segments | Januvia
Segment Reporting Information [Line Items]
Sales	809	774
Total Pharmaceutical segment sales | Operating Segments | Janumet
Segment Reporting Information [Line Items]
Sales	486	503
Total Pharmaceutical segment sales | Operating Segments | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	183	195
Total Pharmaceutical segment sales | Operating Segments | NuvaRing
Segment Reporting Information [Line Items]
Sales	45	63
Total Pharmaceutical segment sales | Operating Segments | Singulair
Segment Reporting Information [Line Items]
Sales	107	155
Total Pharmaceutical segment sales | Operating Segments | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	90	102
Total Pharmaceutical segment sales | Operating Segments | Arcoxia
Segment Reporting Information [Line Items]
Sales	56	70
Total Pharmaceutical segment sales | Operating Segments | Follistim AQ
Segment Reporting Information [Line Items]
Sales	52	41
Total Pharmaceutical segment sales | Operating Segments | Nasonex
Segment Reporting Information [Line Items]
Sales	43	71
Total Pharmaceutical segment sales | Operating Segments | Other pharmaceutical (3)
Segment Reporting Information [Line Items]
Sales	1,197	1,338
Total Pharmaceutical segment sales | United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	4,641	4,714
Total Pharmaceutical segment sales | United States | Operating Segments | Keytruda
Segment Reporting Information [Line Items]
Sales	2,181	1,906
Total Pharmaceutical segment sales | United States | Operating Segments | Alliance revenue - Lynparza (1)
Segment Reporting Information [Line Items]
Sales	118	85
Total Pharmaceutical segment sales | United States | Operating Segments | Alliance revenue - Lenvima (1)
Segment Reporting Information [Line Items]
Sales	85	90
Total Pharmaceutical segment sales | United States | Operating Segments | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	313	461
Total Pharmaceutical segment sales | United States | Operating Segments | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	333	333
Total Pharmaceutical segment sales | United States | Operating Segments | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	73	182
Total Pharmaceutical segment sales | United States | Operating Segments | RotaTeq
Segment Reporting Information [Line Items]
Sales	118	140
Total Pharmaceutical segment sales | United States | Operating Segments | Vaqta
Segment Reporting Information [Line Items]
Sales	25	30
Total Pharmaceutical segment sales | United States | Operating Segments | Bridion
Segment Reporting Information [Line Items]
Sales	167	143
Total Pharmaceutical segment sales | United States | Operating Segments | Prevymis
Segment Reporting Information [Line Items]
Sales	35	26
Total Pharmaceutical segment sales | United States | Operating Segments | Noxafil
Segment Reporting Information [Line Items]
Sales	15	8
Total Pharmaceutical segment sales | United States | Operating Segments | Primaxin
Segment Reporting Information [Line Items]
Sales	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Cancidas
Segment Reporting Information [Line Items]
Sales	3	3
Total Pharmaceutical segment sales | United States | Operating Segments | Invanz
Segment Reporting Information [Line Items]
Sales	4	6
Total Pharmaceutical segment sales | United States | Operating Segments | Zerbaxa
Segment Reporting Information [Line Items]
Sales	(2)	20
Total Pharmaceutical segment sales | United States | Operating Segments | Simponi
Segment Reporting Information [Line Items]
Sales	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Remicade
Segment Reporting Information [Line Items]
Sales	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Belsomra
Segment Reporting Information [Line Items]
Sales	18	27
Total Pharmaceutical segment sales | United States | Operating Segments | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	71	75
Total Pharmaceutical segment sales | United States | Operating Segments | Zetia
Segment Reporting Information [Line Items]
Sales	2	(2)
Total Pharmaceutical segment sales | United States | Operating Segments | Vytorin
Segment Reporting Information [Line Items]
Sales	2	3
Total Pharmaceutical segment sales | United States | Operating Segments | Atozet
Segment Reporting Information [Line Items]
Sales	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Alliance revenue - Adempas (2)
Segment Reporting Information [Line Items]
Sales	68	49
Total Pharmaceutical segment sales | United States | Operating Segments | Adempas
Segment Reporting Information [Line Items]
Sales	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Januvia
Segment Reporting Information [Line Items]
Sales	348	355
Total Pharmaceutical segment sales | United States | Operating Segments | Janumet
Segment Reporting Information [Line Items]
Sales	84	113
Total Pharmaceutical segment sales | United States | Operating Segments | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	141	149
Total Pharmaceutical segment sales | United States | Operating Segments | NuvaRing
Segment Reporting Information [Line Items]
Sales	21	26
Total Pharmaceutical segment sales | United States | Operating Segments | Singulair
Segment Reporting Information [Line Items]
Sales	4	5
Total Pharmaceutical segment sales | United States | Operating Segments | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	3	7
Total Pharmaceutical segment sales | United States | Operating Segments | Arcoxia
Segment Reporting Information [Line Items]
Sales	0	0
Total Pharmaceutical segment sales | United States | Operating Segments | Follistim AQ
Segment Reporting Information [Line Items]
Sales	25	21
Total Pharmaceutical segment sales | United States | Operating Segments | Nasonex
Segment Reporting Information [Line Items]
Sales	2	6
Total Pharmaceutical segment sales | United States | Operating Segments | Other pharmaceutical (3)
Segment Reporting Information [Line Items]
Sales	384	447
Total Pharmaceutical segment sales | International | Operating Segments
Segment Reporting Information [Line Items]
Sales	6,034	5,941
Total Pharmaceutical segment sales | International | Operating Segments | Keytruda
Segment Reporting Information [Line Items]
Sales	1,718	1,378
Total Pharmaceutical segment sales | International | Operating Segments | Alliance revenue - Lynparza (1)
Segment Reporting Information [Line Items]
Sales	110	60
Total Pharmaceutical segment sales | International | Operating Segments | Alliance revenue - Lenvima (1)
Segment Reporting Information [Line Items]
Sales	44	38
Total Pharmaceutical segment sales | International | Operating Segments | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	604	636
Total Pharmaceutical segment sales | International | Operating Segments | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	117	102
Total Pharmaceutical segment sales | International | Operating Segments | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	99	75
Total Pharmaceutical segment sales | International | Operating Segments | RotaTeq
Segment Reporting Information [Line Items]
Sales	41	82
Total Pharmaceutical segment sales | International | Operating Segments | Vaqta
Segment Reporting Information [Line Items]
Sales	9	30
Total Pharmaceutical segment sales | International | Operating Segments | Bridion
Segment Reporting Information [Line Items]
Sales	173	157
Total Pharmaceutical segment sales | International | Operating Segments | Prevymis
Segment Reporting Information [Line Items]
Sales	47	33
Total Pharmaceutical segment sales | International | Operating Segments | Noxafil
Segment Reporting Information [Line Items]
Sales	52	87
Total Pharmaceutical segment sales | International | Operating Segments | Primaxin
Segment Reporting Information [Line Items]
Sales	65	51
Total Pharmaceutical segment sales | International | Operating Segments | Cancidas
Segment Reporting Information [Line Items]
Sales	55	52
Total Pharmaceutical segment sales | International | Operating Segments | Invanz
Segment Reporting Information [Line Items]
Sales	52	59
Total Pharmaceutical segment sales | International | Operating Segments | Zerbaxa
Segment Reporting Information [Line Items]
Sales	(6)	16
Total Pharmaceutical segment sales | International | Operating Segments | Simponi
Segment Reporting Information [Line Items]
Sales	214	215
Total Pharmaceutical segment sales | International | Operating Segments | Remicade
Segment Reporting Information [Line Items]
Sales	85	88
Total Pharmaceutical segment sales | International | Operating Segments | Belsomra
Segment Reporting Information [Line Items]
Sales	61	53
Total Pharmaceutical segment sales | International | Operating Segments | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	138	170
Total Pharmaceutical segment sales | International | Operating Segments | Zetia
Segment Reporting Information [Line Items]
Sales	90	147
Total Pharmaceutical segment sales | International | Operating Segments | Vytorin
Segment Reporting Information [Line Items]
Sales	38	50
Total Pharmaceutical segment sales | International | Operating Segments | Atozet
Segment Reporting Information [Line Items]
Sales	112	122
Total Pharmaceutical segment sales | International | Operating Segments | Alliance revenue - Adempas (2)
Segment Reporting Information [Line Items]
Sales	6	5
Total Pharmaceutical segment sales | International | Operating Segments | Adempas
Segment Reporting Information [Line Items]
Sales	55	56
Total Pharmaceutical segment sales | International | Operating Segments | Januvia
Segment Reporting Information [Line Items]
Sales	461	419
Total Pharmaceutical segment sales | International | Operating Segments | Janumet
Segment Reporting Information [Line Items]
Sales	401	390
Total Pharmaceutical segment sales | International | Operating Segments | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	42	45
Total Pharmaceutical segment sales | International | Operating Segments | NuvaRing
Segment Reporting Information [Line Items]
Sales	24	37
Total Pharmaceutical segment sales | International | Operating Segments | Singulair
Segment Reporting Information [Line Items]
Sales	102	151
Total Pharmaceutical segment sales | International | Operating Segments | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	87	95
Total Pharmaceutical segment sales | International | Operating Segments | Arcoxia
Segment Reporting Information [Line Items]
Sales	56	70
Total Pharmaceutical segment sales | International | Operating Segments | Follistim AQ
Segment Reporting Information [Line Items]
Sales	27	21
Total Pharmaceutical segment sales | International | Operating Segments | Nasonex
Segment Reporting Information [Line Items]
Sales	41	65
Total Pharmaceutical segment sales | International | Operating Segments | Other pharmaceutical (3)
Segment Reporting Information [Line Items]
Sales	814	886
Total Animal Health segment sales | Operating Segments
Segment Reporting Information [Line Items]
Sales	1,418	1,214
Total Animal Health segment sales | Operating Segments | Livestock
Segment Reporting Information [Line Items]
Sales	819	739
Total Animal Health segment sales | Operating Segments | Companion Animals
Segment Reporting Information [Line Items]
Sales	599	475
Total Animal Health segment sales | United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	437	384
Total Animal Health segment sales | United States | Operating Segments | Livestock
Segment Reporting Information [Line Items]
Sales	157	162
Total Animal Health segment sales | United States | Operating Segments | Companion Animals
Segment Reporting Information [Line Items]
Sales	280	222
Total Animal Health segment sales | International | Operating Segments
Segment Reporting Information [Line Items]
Sales	981	830
Total Animal Health segment sales | International | Operating Segments | Livestock
Segment Reporting Information [Line Items]
Sales	662	577
Total Animal Health segment sales | International | Operating Segments | Companion Animals
Segment Reporting Information [Line Items]
Sales	319	253
Other segment sales (4) | Operating Segments
Segment Reporting Information [Line Items]
Sales	0	23
Other segment sales (4) | United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	0	23
Other segment sales (4) | International | Operating Segments
Segment Reporting Information [Line Items]
Sales	$ 0	$ 0

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