Segment Reporting - Sales from Products (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Sales	$ 13,154	$ 10,929	$ 35,183	$ 30,570
Revenue related to the sale of the marketing rights	135		185
Operating Segments
Segment Reporting Information [Line Items]
Sales	12,913	10,934	35,021	30,355
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Sales	241	(5)	162	215
United States
Segment Reporting Information [Line Items]
Sales	6,276	5,250	16,166	14,301
United States \| Operating Segments
Segment Reporting Information [Line Items]
Sales	6,137	5,241	15,974	14,255
United States \| Corporate, Non-Segment
Segment Reporting Information [Line Items]
Sales	139	9	192	46
Int’l
Segment Reporting Information [Line Items]
Sales	6,878	5,679	19,017	16,269
Int’l \| Operating Segments
Segment Reporting Information [Line Items]
Sales	6,777	5,693	19,047	16,101
Int’l \| Corporate, Non-Segment
Segment Reporting Information [Line Items]
Sales	101	(14)	(30)	168
Pharmaceutical \| Operating Segments
Segment Reporting Information [Line Items]
Sales	11,496	9,714	30,714	26,797
Pharmaceutical \| Operating Segments \| Keytruda
Segment Reporting Information [Line Items]
Sales	4,534	3,715	12,609	10,387
Pharmaceutical \| Operating Segments \| Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	246	196	721	519
Pharmaceutical \| Operating Segments \| Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	188	142	498	421
Pharmaceutical \| Operating Segments \| Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,993	1,187	4,144	2,941
Pharmaceutical \| Operating Segments \| ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	661	576	1,626	1,390
Pharmaceutical \| Operating Segments \| Pneumovax 23
Segment Reporting Information [Line Items]
Sales	277	375	600	748
Pharmaceutical \| Operating Segments \| RotaTeq
Segment Reporting Information [Line Items]
Sales	227	210	593	601
Pharmaceutical \| Operating Segments \| Vaqta
Segment Reporting Information [Line Items]
Sales	48	51	138	139
Pharmaceutical \| Operating Segments \| Bridion
Segment Reporting Information [Line Items]
Sales	369	320	1,096	843
Pharmaceutical \| Operating Segments \| Prevymis
Segment Reporting Information [Line Items]
Sales	96	77	270	200
Pharmaceutical \| Operating Segments \| Noxafil
Segment Reporting Information [Line Items]
Sales	64	79	197	247
Pharmaceutical \| Operating Segments \| Primaxin
Segment Reporting Information [Line Items]
Sales	70	74	194	189
Pharmaceutical \| Operating Segments \| Cancidas
Segment Reporting Information [Line Items]
Sales	56	50	168	148
Pharmaceutical \| Operating Segments \| Invanz
Segment Reporting Information [Line Items]
Sales	53	51	157	159
Pharmaceutical \| Operating Segments \| Zerbaxa
Segment Reporting Information [Line Items]
Sales	(2)	43	(11)	112
Pharmaceutical \| Operating Segments \| Simponi
Segment Reporting Information [Line Items]
Sales	203	209	619	615
Pharmaceutical \| Operating Segments \| Remicade
Segment Reporting Information [Line Items]
Sales	73	82	233	242
Pharmaceutical \| Operating Segments \| Belsomra
Segment Reporting Information [Line Items]
Sales	81	81	238	244
Pharmaceutical \| Operating Segments \| Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	189	205	590	646
Pharmaceutical \| Operating Segments \| Alliance revenue-Adempas/Verquvo
Segment Reporting Information [Line Items]
Sales	100	83	248	216
Pharmaceutical \| Operating Segments \| Adempas
Segment Reporting Information [Line Items]
Sales	59	55	188	167
Pharmaceutical \| Operating Segments \| Januvia
Segment Reporting Information [Line Items]
Sales	852	821	2,445	2,449
Pharmaceutical \| Operating Segments \| Janumet
Segment Reporting Information [Line Items]
Sales	487	506	1,449	1,499
Pharmaceutical \| Operating Segments \| Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	572	526	1,704	1,675
Pharmaceutical \| United States \| Operating Segments
Segment Reporting Information [Line Items]
Sales	5,670	4,842	14,611	13,108
Pharmaceutical \| United States \| Operating Segments \| Keytruda
Segment Reporting Information [Line Items]
Sales	2,580	2,157	7,108	6,106
Pharmaceutical \| United States \| Operating Segments \| Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	129	107	371	297
Pharmaceutical \| United States \| Operating Segments \| Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	114	82	287	270
Pharmaceutical \| United States \| Operating Segments \| Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	839	579	1,605	1,209
Pharmaceutical \| United States \| Operating Segments \| ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	537	437	1,255	1,033
Pharmaceutical \| United States \| Operating Segments \| Pneumovax 23
Segment Reporting Information [Line Items]
Sales	181	276	354	478
Pharmaceutical \| United States \| Operating Segments \| RotaTeq
Segment Reporting Information [Line Items]
Sales	135	114	364	355
Pharmaceutical \| United States \| Operating Segments \| Vaqta
Segment Reporting Information [Line Items]
Sales	32	32	80	79
Pharmaceutical \| United States \| Operating Segments \| Bridion
Segment Reporting Information [Line Items]
Sales	181	162	545	412
Pharmaceutical \| United States \| Operating Segments \| Prevymis
Segment Reporting Information [Line Items]
Sales	39	32	111	87
Pharmaceutical \| United States \| Operating Segments \| Noxafil
Segment Reporting Information [Line Items]
Sales	19	13	48	27
Pharmaceutical \| United States \| Operating Segments \| Primaxin
Segment Reporting Information [Line Items]
Sales	0	1	0	2
Pharmaceutical \| United States \| Operating Segments \| Cancidas
Segment Reporting Information [Line Items]
Sales	1	1	4	2
Pharmaceutical \| United States \| Operating Segments \| Invanz
Segment Reporting Information [Line Items]
Sales	(2)	1	(2)	7
Pharmaceutical \| United States \| Operating Segments \| Zerbaxa
Segment Reporting Information [Line Items]
Sales	(1)	20	(5)	57
Pharmaceutical \| United States \| Operating Segments \| Simponi
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Pharmaceutical \| United States \| Operating Segments \| Remicade
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Pharmaceutical \| United States \| Operating Segments \| Belsomra
Segment Reporting Information [Line Items]
Sales	23	18	56	67
Pharmaceutical \| United States \| Operating Segments \| Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	77	92	222	243
Pharmaceutical \| United States \| Operating Segments \| Alliance revenue-Adempas/Verquvo
Segment Reporting Information [Line Items]
Sales	73	78	222	200
Pharmaceutical \| United States \| Operating Segments \| Adempas
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Pharmaceutical \| United States \| Operating Segments \| Januvia
Segment Reporting Information [Line Items]
Sales	365	342	997	1,110
Pharmaceutical \| United States \| Operating Segments \| Janumet
Segment Reporting Information [Line Items]
Sales	86	105	244	361
Pharmaceutical \| United States \| Operating Segments \| Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	262	193	745	706
Pharmaceutical \| Int’l \| Operating Segments
Segment Reporting Information [Line Items]
Sales	5,826	4,872	16,103	13,690
Pharmaceutical \| Int’l \| Operating Segments \| Keytruda
Segment Reporting Information [Line Items]
Sales	1,954	1,559	5,501	4,281
Pharmaceutical \| Int’l \| Operating Segments \| Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	117	89	350	223
Pharmaceutical \| Int’l \| Operating Segments \| Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	74	60	211	152
Pharmaceutical \| Int’l \| Operating Segments \| Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,154	608	2,539	1,732
Pharmaceutical \| Int’l \| Operating Segments \| ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	125	139	371	356
Pharmaceutical \| Int’l \| Operating Segments \| Pneumovax 23
Segment Reporting Information [Line Items]
Sales	97	99	247	270
Pharmaceutical \| Int’l \| Operating Segments \| RotaTeq
Segment Reporting Information [Line Items]
Sales	92	96	229	246
Pharmaceutical \| Int’l \| Operating Segments \| Vaqta
Segment Reporting Information [Line Items]
Sales	16	19	58	60
Pharmaceutical \| Int’l \| Operating Segments \| Bridion
Segment Reporting Information [Line Items]
Sales	188	157	551	431
Pharmaceutical \| Int’l \| Operating Segments \| Prevymis
Segment Reporting Information [Line Items]
Sales	57	46	159	113
Pharmaceutical \| Int’l \| Operating Segments \| Noxafil
Segment Reporting Information [Line Items]
Sales	45	66	149	220
Pharmaceutical \| Int’l \| Operating Segments \| Primaxin
Segment Reporting Information [Line Items]
Sales	69	73	194	187
Pharmaceutical \| Int’l \| Operating Segments \| Cancidas
Segment Reporting Information [Line Items]
Sales	56	49	164	147
Pharmaceutical \| Int’l \| Operating Segments \| Invanz
Segment Reporting Information [Line Items]
Sales	55	50	159	152
Pharmaceutical \| Int’l \| Operating Segments \| Zerbaxa
Segment Reporting Information [Line Items]
Sales	(1)	23	(6)	54
Pharmaceutical \| Int’l \| Operating Segments \| Simponi
Segment Reporting Information [Line Items]
Sales	203	209	619	615
Pharmaceutical \| Int’l \| Operating Segments \| Remicade
Segment Reporting Information [Line Items]
Sales	73	82	233	242
Pharmaceutical \| Int’l \| Operating Segments \| Belsomra
Segment Reporting Information [Line Items]
Sales	58	63	183	177
Pharmaceutical \| Int’l \| Operating Segments \| Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	112	113	368	403
Pharmaceutical \| Int’l \| Operating Segments \| Alliance revenue-Adempas/Verquvo
Segment Reporting Information [Line Items]
Sales	27	5	26	16
Pharmaceutical \| Int’l \| Operating Segments \| Adempas
Segment Reporting Information [Line Items]
Sales	59	55	188	167
Pharmaceutical \| Int’l \| Operating Segments \| Januvia
Segment Reporting Information [Line Items]
Sales	487	479	1,448	1,339
Pharmaceutical \| Int’l \| Operating Segments \| Janumet
Segment Reporting Information [Line Items]
Sales	401	400	1,205	1,138
Pharmaceutical \| Int’l \| Operating Segments \| Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	308	333	957	969
Animal Health \| Operating Segments
Segment Reporting Information [Line Items]
Sales	1,417	1,220	4,307	3,535
Animal Health \| Operating Segments \| Livestock
Segment Reporting Information [Line Items]
Sales	864	758	2,503	2,145
Animal Health \| Operating Segments \| Companion Animals
Segment Reporting Information [Line Items]
Sales	553	462	1,804	1,390
Animal Health \| United States \| Operating Segments
Segment Reporting Information [Line Items]
Sales	467	399	1,363	1,124
Animal Health \| United States \| Operating Segments \| Livestock
Segment Reporting Information [Line Items]
Sales	190	165	508	448
Animal Health \| United States \| Operating Segments \| Companion Animals
Segment Reporting Information [Line Items]
Sales	277	234	855	676
Animal Health \| Int’l \| Operating Segments
Segment Reporting Information [Line Items]
Sales	951	821	2,944	2,411
Animal Health \| Int’l \| Operating Segments \| Livestock
Segment Reporting Information [Line Items]
Sales	675	593	1,996	1,697
Animal Health \| Int’l \| Operating Segments \| Companion Animals
Segment Reporting Information [Line Items]
Sales	276	228	948	714
Other Segments \| Operating Segments
Segment Reporting Information [Line Items]
Sales	0	0	0	23
Other Segments \| United States \| Operating Segments
Segment Reporting Information [Line Items]
Sales	0	0	0	23
Other Segments \| Int’l \| Operating Segments
Segment Reporting Information [Line Items]
Sales	$ 0	$ 0	$ 0	$ 0