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Segment Reporting - Sales of Company's Products (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Sales	$ 47,994	$ 46,840	$ 42,294
Operating Segments
Segment Reporting Information [Line Items]
Sales	47,747	46,319	42,151
Operating Segments | Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	43,021	41,751	37,689
Operating Segments | Pharmaceutical segment | Keytruda
Segment Reporting Information [Line Items]
Sales	14,380	11,084	7,171
Operating Segments | Pharmaceutical segment | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	725	444	187
Operating Segments | Pharmaceutical segment | Alliance revenue - Lenvima (1)
Segment Reporting Information [Line Items]
Sales	580	404	149
Operating Segments | Pharmaceutical segment | Emend
Segment Reporting Information [Line Items]
Sales	145	388	522
Operating Segments | Pharmaceutical segment | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	3,938	3,737	3,151
Operating Segments | Pharmaceutical segment | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	1,878	2,275	1,798
Operating Segments | Pharmaceutical segment | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	1,087	926	907
Operating Segments | Pharmaceutical segment | RotaTeq
Segment Reporting Information [Line Items]
Sales	797	791	728
Operating Segments | Pharmaceutical segment | Vaqta
Segment Reporting Information [Line Items]
Sales	170	238	239
Operating Segments | Pharmaceutical segment | Bridion
Segment Reporting Information [Line Items]
Sales	1,198	1,131	917
Operating Segments | Pharmaceutical segment | Noxafil
Segment Reporting Information [Line Items]
Sales	329	662	742
Operating Segments | Pharmaceutical segment | Prevymis
Segment Reporting Information [Line Items]
Sales	281	165	72
Operating Segments | Pharmaceutical segment | Primaxin
Segment Reporting Information [Line Items]
Sales	251	273	265
Operating Segments | Pharmaceutical segment | Cancidas
Segment Reporting Information [Line Items]
Sales	213	249	326
Operating Segments | Pharmaceutical segment | Invanz
Segment Reporting Information [Line Items]
Sales	211	263	496
Operating Segments | Pharmaceutical segment | Cubicin
Segment Reporting Information [Line Items]
Sales	152	257	367
Operating Segments | Pharmaceutical segment | Zerbaxa
Segment Reporting Information [Line Items]
Sales	130	121	87
Operating Segments | Pharmaceutical segment | Simponi
Segment Reporting Information [Line Items]
Sales	838	830	893
Operating Segments | Pharmaceutical segment | Remicade
Segment Reporting Information [Line Items]
Sales	330	411	582
Operating Segments | Pharmaceutical segment | Belsomra
Segment Reporting Information [Line Items]
Sales	327	306	260
Operating Segments | Pharmaceutical segment | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	857	975	1,140
Operating Segments | Pharmaceutical segment | Zepatier
Segment Reporting Information [Line Items]
Sales	167	370	455
Operating Segments | Pharmaceutical segment | Zetia
Segment Reporting Information [Line Items]
Sales	482	590	857
Operating Segments | Pharmaceutical segment | Vytorin
Segment Reporting Information [Line Items]
Sales	182	285	497
Operating Segments | Pharmaceutical segment | Atozet
Segment Reporting Information [Line Items]
Sales	453	391	347
Operating Segments | Pharmaceutical segment | Alliance revenue - Adempas (2)
Segment Reporting Information [Line Items]
Sales	281	204	139
Operating Segments | Pharmaceutical segment | Adempas
Segment Reporting Information [Line Items]
Sales	220	215	190
Operating Segments | Pharmaceutical segment | Januvia
Segment Reporting Information [Line Items]
Sales	3,306	3,482	3,686
Operating Segments | Pharmaceutical segment | Janumet
Segment Reporting Information [Line Items]
Sales	1,971	2,041	2,228
Operating Segments | Pharmaceutical segment | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	680	787	703
Operating Segments | Pharmaceutical segment | NuvaRing
Segment Reporting Information [Line Items]
Sales	236	879	902
Operating Segments | Pharmaceutical segment | Singulair
Segment Reporting Information [Line Items]
Sales	462	698	708
Operating Segments | Pharmaceutical segment | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	386	442	453
Operating Segments | Pharmaceutical segment | Arcoxia
Segment Reporting Information [Line Items]
Sales	258	288	335
Operating Segments | Pharmaceutical segment | Nasonex
Segment Reporting Information [Line Items]
Sales	218	293	376
Operating Segments | Pharmaceutical segment | Follistim AQ
Segment Reporting Information [Line Items]
Sales	193	241	268
Operating Segments | Pharmaceutical segment | Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	4,709	4,615	4,546
Operating Segments | Animal Health
Segment Reporting Information [Line Items]
Sales	4,703	4,393	4,212
Operating Segments | Animal Health | Livestock
Segment Reporting Information [Line Items]
Sales	2,939	2,784	2,630
Operating Segments | Animal Health | Companion Animals
Segment Reporting Information [Line Items]
Sales	1,764	1,609	1,582
Operating Segments | Other segments
Segment Reporting Information [Line Items]
Sales	23	175	250
Other
Segment Reporting Information [Line Items]
Sales	247	521	143
United States
Segment Reporting Information [Line Items]
Sales	21,027	20,519	18,346
United States | Operating Segments
Segment Reporting Information [Line Items]
Sales	20,956	20,433	18,228
United States | Operating Segments | Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	19,449	18,953	16,742
United States | Operating Segments | Pharmaceutical segment | Keytruda
Segment Reporting Information [Line Items]
Sales	8,352	6,305	4,150
United States | Operating Segments | Pharmaceutical segment | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	417	269	127
United States | Operating Segments | Pharmaceutical segment | Alliance revenue - Lenvima (1)
Segment Reporting Information [Line Items]
Sales	359	239	95
United States | Operating Segments | Pharmaceutical segment | Emend
Segment Reporting Information [Line Items]
Sales	18	183	312
United States | Operating Segments | Pharmaceutical segment | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,755	1,831	1,873
United States | Operating Segments | Pharmaceutical segment | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	1,378	1,683	1,430
United States | Operating Segments | Pharmaceutical segment | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	727	679	627
United States | Operating Segments | Pharmaceutical segment | RotaTeq
Segment Reporting Information [Line Items]
Sales	486	506	496
United States | Operating Segments | Pharmaceutical segment | Vaqta
Segment Reporting Information [Line Items]
Sales	103	130	127
United States | Operating Segments | Pharmaceutical segment | Bridion
Segment Reporting Information [Line Items]
Sales	583	533	386
United States | Operating Segments | Pharmaceutical segment | Noxafil
Segment Reporting Information [Line Items]
Sales	42	282	353
United States | Operating Segments | Pharmaceutical segment | Prevymis
Segment Reporting Information [Line Items]
Sales	119	84	46
United States | Operating Segments | Pharmaceutical segment | Primaxin
Segment Reporting Information [Line Items]
Sales	2	2	7
United States | Operating Segments | Pharmaceutical segment | Cancidas
Segment Reporting Information [Line Items]
Sales	7	6	12
United States | Operating Segments | Pharmaceutical segment | Invanz
Segment Reporting Information [Line Items]
Sales	9	30	253
United States | Operating Segments | Pharmaceutical segment | Cubicin
Segment Reporting Information [Line Items]
Sales	46	92	191
United States | Operating Segments | Pharmaceutical segment | Zerbaxa
Segment Reporting Information [Line Items]
Sales	74	63	42
United States | Operating Segments | Pharmaceutical segment | Simponi
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Remicade
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Belsomra
Segment Reporting Information [Line Items]
Sales	81	92	96
United States | Operating Segments | Pharmaceutical segment | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	326	398	513
United States | Operating Segments | Pharmaceutical segment | Zepatier
Segment Reporting Information [Line Items]
Sales	60	118	8
United States | Operating Segments | Pharmaceutical segment | Zetia
Segment Reporting Information [Line Items]
Sales	(1)	14	45
United States | Operating Segments | Pharmaceutical segment | Vytorin
Segment Reporting Information [Line Items]
Sales	12	16	10
United States | Operating Segments | Pharmaceutical segment | Atozet
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Alliance revenue - Adempas (2)
Segment Reporting Information [Line Items]
Sales	259	194	134
United States | Operating Segments | Pharmaceutical segment | Adempas
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Januvia
Segment Reporting Information [Line Items]
Sales	1,470	1,724	1,969
United States | Operating Segments | Pharmaceutical segment | Janumet
Segment Reporting Information [Line Items]
Sales	477	589	811
United States | Operating Segments | Pharmaceutical segment | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	488	568	495
United States | Operating Segments | Pharmaceutical segment | NuvaRing
Segment Reporting Information [Line Items]
Sales	110	742	722
United States | Operating Segments | Pharmaceutical segment | Singulair
Segment Reporting Information [Line Items]
Sales	18	29	20
United States | Operating Segments | Pharmaceutical segment | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	21	24	23
United States | Operating Segments | Pharmaceutical segment | Arcoxia
Segment Reporting Information [Line Items]
Sales	0	0	0
United States | Operating Segments | Pharmaceutical segment | Nasonex
Segment Reporting Information [Line Items]
Sales	12	9	23
United States | Operating Segments | Pharmaceutical segment | Follistim AQ
Segment Reporting Information [Line Items]
Sales	84	103	115
United States | Operating Segments | Pharmaceutical segment | Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	1,555	1,416	1,231
United States | Operating Segments | Animal Health
Segment Reporting Information [Line Items]
Sales	1,484	1,306	1,238
United States | Operating Segments | Animal Health | Livestock
Segment Reporting Information [Line Items]
Sales	612	582	528
United States | Operating Segments | Animal Health | Companion Animals
Segment Reporting Information [Line Items]
Sales	872	724	710
United States | Operating Segments | Other segments
Segment Reporting Information [Line Items]
Sales	23	174	248
United States | Other
Segment Reporting Information [Line Items]
Sales	71	86	118
Int’l
Segment Reporting Information [Line Items]
Sales	26,967	26,321	23,949
Int’l | Operating Segments
Segment Reporting Information [Line Items]
Sales	26,791	25,885	23,923
Int’l | Operating Segments | Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	23,572	22,798	20,947
Int’l | Operating Segments | Pharmaceutical segment | Keytruda
Segment Reporting Information [Line Items]
Sales	6,028	4,779	3,021
Int’l | Operating Segments | Pharmaceutical segment | Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	308	176	61
Int’l | Operating Segments | Pharmaceutical segment | Alliance revenue - Lenvima (1)
Segment Reporting Information [Line Items]
Sales	220	165	54
Int’l | Operating Segments | Pharmaceutical segment | Emend
Segment Reporting Information [Line Items]
Sales	127	205	210
Int’l | Operating Segments | Pharmaceutical segment | Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	2,184	1,905	1,279
Int’l | Operating Segments | Pharmaceutical segment | ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	500	592	368
Int’l | Operating Segments | Pharmaceutical segment | Pneumovax 23
Segment Reporting Information [Line Items]
Sales	359	247	281
Int’l | Operating Segments | Pharmaceutical segment | RotaTeq
Segment Reporting Information [Line Items]
Sales	311	284	232
Int’l | Operating Segments | Pharmaceutical segment | Vaqta
Segment Reporting Information [Line Items]
Sales	67	108	112
Int’l | Operating Segments | Pharmaceutical segment | Bridion
Segment Reporting Information [Line Items]
Sales	615	598	531
Int’l | Operating Segments | Pharmaceutical segment | Noxafil
Segment Reporting Information [Line Items]
Sales	287	380	389
Int’l | Operating Segments | Pharmaceutical segment | Prevymis
Segment Reporting Information [Line Items]
Sales	162	81	27
Int’l | Operating Segments | Pharmaceutical segment | Primaxin
Segment Reporting Information [Line Items]
Sales	248	271	258
Int’l | Operating Segments | Pharmaceutical segment | Cancidas
Segment Reporting Information [Line Items]
Sales	207	242	314
Int’l | Operating Segments | Pharmaceutical segment | Invanz
Segment Reporting Information [Line Items]
Sales	202	233	243
Int’l | Operating Segments | Pharmaceutical segment | Cubicin
Segment Reporting Information [Line Items]
Sales	106	165	176
Int’l | Operating Segments | Pharmaceutical segment | Zerbaxa
Segment Reporting Information [Line Items]
Sales	56	58	45
Int’l | Operating Segments | Pharmaceutical segment | Simponi
Segment Reporting Information [Line Items]
Sales	838	830	893
Int’l | Operating Segments | Pharmaceutical segment | Remicade
Segment Reporting Information [Line Items]
Sales	330	411	582
Int’l | Operating Segments | Pharmaceutical segment | Belsomra
Segment Reporting Information [Line Items]
Sales	247	214	164
Int’l | Operating Segments | Pharmaceutical segment | Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	531	576	627
Int’l | Operating Segments | Pharmaceutical segment | Zepatier
Segment Reporting Information [Line Items]
Sales	107	252	447
Int’l | Operating Segments | Pharmaceutical segment | Zetia
Segment Reporting Information [Line Items]
Sales	483	575	813
Int’l | Operating Segments | Pharmaceutical segment | Vytorin
Segment Reporting Information [Line Items]
Sales	171	269	487
Int’l | Operating Segments | Pharmaceutical segment | Atozet
Segment Reporting Information [Line Items]
Sales	453	391	347
Int’l | Operating Segments | Pharmaceutical segment | Alliance revenue - Adempas (2)
Segment Reporting Information [Line Items]
Sales	22	10	5
Int’l | Operating Segments | Pharmaceutical segment | Adempas
Segment Reporting Information [Line Items]
Sales	220	215	190
Int’l | Operating Segments | Pharmaceutical segment | Januvia
Segment Reporting Information [Line Items]
Sales	1,836	1,758	1,718
Int’l | Operating Segments | Pharmaceutical segment | Janumet
Segment Reporting Information [Line Items]
Sales	1,494	1,452	1,417
Int’l | Operating Segments | Pharmaceutical segment | Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	192	219	208
Int’l | Operating Segments | Pharmaceutical segment | NuvaRing
Segment Reporting Information [Line Items]
Sales	127	136	180
Int’l | Operating Segments | Pharmaceutical segment | Singulair
Segment Reporting Information [Line Items]
Sales	444	669	688
Int’l | Operating Segments | Pharmaceutical segment | Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	365	418	431
Int’l | Operating Segments | Pharmaceutical segment | Arcoxia
Segment Reporting Information [Line Items]
Sales	258	288	335
Int’l | Operating Segments | Pharmaceutical segment | Nasonex
Segment Reporting Information [Line Items]
Sales	206	284	353
Int’l | Operating Segments | Pharmaceutical segment | Follistim AQ
Segment Reporting Information [Line Items]
Sales	109	138	153
Int’l | Operating Segments | Pharmaceutical segment | Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	3,152	3,204	3,308
Int’l | Operating Segments | Animal Health
Segment Reporting Information [Line Items]
Sales	3,219	3,086	2,974
Int’l | Operating Segments | Animal Health | Livestock
Segment Reporting Information [Line Items]
Sales	2,327	2,201	2,102
Int’l | Operating Segments | Animal Health | Companion Animals
Segment Reporting Information [Line Items]
Sales	892	885	872
Int’l | Operating Segments | Other segments
Segment Reporting Information [Line Items]
Sales	0	1	2
Int’l | Other
Segment Reporting Information [Line Items]
Sales	$ 176	$ 436	$ 26

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