Segment Reporting - Sales of Company's Products (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Sales	$ 42,294	$ 40,122	$ 39,807
Proceeds from sale of intangible assets	95	85	170
Operating Segments
Segment Reporting Information [Line Items]
Sales	42,151	39,662	39,014
Operating Segments \| Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	37,689	35,390	35,151
Operating Segments \| Pharmaceutical segment \| Keytruda
Segment Reporting Information [Line Items]
Sales	7,171	3,809	1,402
Operating Segments \| Pharmaceutical segment \| Emend
Segment Reporting Information [Line Items]
Sales	522	556	549
Operating Segments \| Pharmaceutical segment \| Temodar
Segment Reporting Information [Line Items]
Sales	214	271	283
Operating Segments \| Pharmaceutical segment \| Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	187	20	0
Operating Segments \| Pharmaceutical segment \| Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	149	0	0
Operating Segments \| Pharmaceutical segment \| Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	3,151	2,308	2,173
Operating Segments \| Pharmaceutical segment \| ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	1,798	1,676	1,640
Operating Segments \| Pharmaceutical segment \| Pneumovax 23
Segment Reporting Information [Line Items]
Sales	907	821	641
Operating Segments \| Pharmaceutical segment \| RotaTeq
Segment Reporting Information [Line Items]
Sales	728	686	652
Operating Segments \| Pharmaceutical segment \| Zostavax
Segment Reporting Information [Line Items]
Sales	217	668	685
Operating Segments \| Pharmaceutical segment \| Bridion
Segment Reporting Information [Line Items]
Sales	917	704	482
Operating Segments \| Pharmaceutical segment \| Noxafil
Segment Reporting Information [Line Items]
Sales	742	636	595
Operating Segments \| Pharmaceutical segment \| Invanz
Segment Reporting Information [Line Items]
Sales	496	602	561
Operating Segments \| Pharmaceutical segment \| Cubicin
Segment Reporting Information [Line Items]
Sales	367	382	1,087
Operating Segments \| Pharmaceutical segment \| Cancidas
Segment Reporting Information [Line Items]
Sales	326	422	558
Operating Segments \| Pharmaceutical segment \| Primaxin
Segment Reporting Information [Line Items]
Sales	265	280	297
Operating Segments \| Pharmaceutical segment \| Simponi
Segment Reporting Information [Line Items]
Sales	893	819	766
Operating Segments \| Pharmaceutical segment \| Remicade
Segment Reporting Information [Line Items]
Sales	582	837	1,268
Operating Segments \| Pharmaceutical segment \| Belsomra
Segment Reporting Information [Line Items]
Sales	260	210	154
Operating Segments \| Pharmaceutical segment \| Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	1,140	1,204	1,387
Operating Segments \| Pharmaceutical segment \| Zepatier
Segment Reporting Information [Line Items]
Sales	455	1,660	555
Operating Segments \| Pharmaceutical segment \| Zetia
Segment Reporting Information [Line Items]
Sales	857	1,344	2,560
Operating Segments \| Pharmaceutical segment \| Vytorin
Segment Reporting Information [Line Items]
Sales	497	751	1,141
Operating Segments \| Pharmaceutical segment \| Atozet
Segment Reporting Information [Line Items]
Sales	347	225	146
Operating Segments \| Pharmaceutical segment \| Adempas
Segment Reporting Information [Line Items]
Sales	329	300	169
Operating Segments \| Pharmaceutical segment \| Januvia
Segment Reporting Information [Line Items]
Sales	3,686	3,737	3,908
Operating Segments \| Pharmaceutical segment \| Janumet
Segment Reporting Information [Line Items]
Sales	2,228	2,158	2,201
Operating Segments \| Pharmaceutical segment \| NuvaRing
Segment Reporting Information [Line Items]
Sales	902	761	777
Operating Segments \| Pharmaceutical segment \| Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	703	686	606
Operating Segments \| Pharmaceutical segment \| Singulair
Segment Reporting Information [Line Items]
Sales	708	732	915
Operating Segments \| Pharmaceutical segment \| Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	453	484	511
Operating Segments \| Pharmaceutical segment \| Nasonex
Segment Reporting Information [Line Items]
Sales	376	387	537
Operating Segments \| Pharmaceutical segment \| Arcoxia
Segment Reporting Information [Line Items]
Sales	335	363	450
Operating Segments \| Pharmaceutical segment \| Follistim AQ
Segment Reporting Information [Line Items]
Sales	268	298	355
Operating Segments \| Pharmaceutical segment \| Dulera
Segment Reporting Information [Line Items]
Sales	214	287	436
Operating Segments \| Pharmaceutical segment \| Fosamax
Segment Reporting Information [Line Items]
Sales	209	241	284
Operating Segments \| Pharmaceutical segment \| Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	4,090	4,065	4,420
Operating Segments \| Animal Health
Segment Reporting Information [Line Items]
Sales	4,212	3,875	3,478
Operating Segments \| Animal Health \| Livestock
Segment Reporting Information [Line Items]
Sales	2,630	2,484	2,287
Operating Segments \| Animal Health \| Companion Animals
Segment Reporting Information [Line Items]
Sales	1,582	1,391	1,191
Operating Segments \| Other segments
Segment Reporting Information [Line Items]
Sales	250	397	385
Other
Segment Reporting Information [Line Items]
Sales	143	460	793
United States
Segment Reporting Information [Line Items]
Sales	18,212	17,424	18,478
United States \| Operating Segments
Segment Reporting Information [Line Items]
Sales	18,094	17,340	18,447
United States \| Operating Segments \| Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	16,608	15,854	17,073
United States \| Operating Segments \| Pharmaceutical segment \| Keytruda
Segment Reporting Information [Line Items]
Sales	4,150	2,309	792
United States \| Operating Segments \| Pharmaceutical segment \| Emend
Segment Reporting Information [Line Items]
Sales	312	342	356
United States \| Operating Segments \| Pharmaceutical segment \| Temodar
Segment Reporting Information [Line Items]
Sales	6	16	15
United States \| Operating Segments \| Pharmaceutical segment \| Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	127	0	0
United States \| Operating Segments \| Pharmaceutical segment \| Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	95	0	0
United States \| Operating Segments \| Pharmaceutical segment \| Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,873	1,565	1,780
United States \| Operating Segments \| Pharmaceutical segment \| ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	1,430	1,374	1,362
United States \| Operating Segments \| Pharmaceutical segment \| Pneumovax 23
Segment Reporting Information [Line Items]
Sales	627	581	447
United States \| Operating Segments \| Pharmaceutical segment \| RotaTeq
Segment Reporting Information [Line Items]
Sales	496	481	482
United States \| Operating Segments \| Pharmaceutical segment \| Zostavax
Segment Reporting Information [Line Items]
Sales	22	422	518
United States \| Operating Segments \| Pharmaceutical segment \| Bridion
Segment Reporting Information [Line Items]
Sales	386	239	77
United States \| Operating Segments \| Pharmaceutical segment \| Noxafil
Segment Reporting Information [Line Items]
Sales	353	309	284
United States \| Operating Segments \| Pharmaceutical segment \| Invanz
Segment Reporting Information [Line Items]
Sales	253	361	329
United States \| Operating Segments \| Pharmaceutical segment \| Cubicin
Segment Reporting Information [Line Items]
Sales	191	189	906
United States \| Operating Segments \| Pharmaceutical segment \| Cancidas
Segment Reporting Information [Line Items]
Sales	12	20	25
United States \| Operating Segments \| Pharmaceutical segment \| Primaxin
Segment Reporting Information [Line Items]
Sales	7	10	4
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	96	98	84
United States \| Operating Segments \| Pharmaceutical segment \| Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	513	565	721
United States \| Operating Segments \| Pharmaceutical segment \| Zepatier
Segment Reporting Information [Line Items]
Sales	8	771	488
United States \| Operating Segments \| Pharmaceutical segment \| Zetia
Segment Reporting Information [Line Items]
Sales	45	352	1,588
United States \| Operating Segments \| Pharmaceutical segment \| Vytorin
Segment Reporting Information [Line Items]
Sales	10	124	473
United States \| Operating Segments \| Pharmaceutical segment \| Atozet
Segment Reporting Information [Line Items]
Sales	0	0	1
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	1,969	2,153	2,286
United States \| Operating Segments \| Pharmaceutical segment \| Janumet
Segment Reporting Information [Line Items]
Sales	811	863	984
United States \| Operating Segments \| Pharmaceutical segment \| NuvaRing
Segment Reporting Information [Line Items]
Sales	722	564	576
United States \| Operating Segments \| Pharmaceutical segment \| Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	495	496	420
United States \| Operating Segments \| Pharmaceutical segment \| Singulair
Segment Reporting Information [Line Items]
Sales	20	40	40
United States \| Operating Segments \| Pharmaceutical segment \| Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	23	18	16
United States \| Operating Segments \| Pharmaceutical segment \| Nasonex
Segment Reporting Information [Line Items]
Sales	23	54	184
United States \| Operating Segments \| Pharmaceutical segment \| Arcoxia
Segment Reporting Information [Line Items]
Sales	0	0	0
United States \| Operating Segments \| Pharmaceutical segment \| Follistim AQ
Segment Reporting Information [Line Items]
Sales	115	123	157
United States \| Operating Segments \| Pharmaceutical segment \| Dulera
Segment Reporting Information [Line Items]
Sales	186	261	412
United States \| Operating Segments \| Pharmaceutical segment \| Fosamax
Segment Reporting Information [Line Items]
Sales	4	6	5
United States \| Operating Segments \| Pharmaceutical segment \| Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	1,228	1,148	1,261
United States \| Operating Segments \| Animal Health
Segment Reporting Information [Line Items]
Sales	1,238	1,090	989
United States \| Operating Segments \| Animal Health \| Livestock
Segment Reporting Information [Line Items]
Sales	528	471	446
United States \| Operating Segments \| Animal Health \| Companion Animals
Segment Reporting Information [Line Items]
Sales	710	619	543
United States \| Operating Segments \| Other segments
Segment Reporting Information [Line Items]
Sales	248	396	385
United States \| Other
Segment Reporting Information [Line Items]
Sales	118	84	31
Int’l
Segment Reporting Information [Line Items]
Sales	24,083	22,698	21,329
Int’l \| Operating Segments
Segment Reporting Information [Line Items]
Sales	24,057	22,322	20,566
Int’l \| Operating Segments \| Pharmaceutical segment
Segment Reporting Information [Line Items]
Sales	21,081	19,536	18,077
Int’l \| Operating Segments \| Pharmaceutical segment \| Keytruda
Segment Reporting Information [Line Items]
Sales	3,021	1,500	610
Int’l \| Operating Segments \| Pharmaceutical segment \| Emend
Segment Reporting Information [Line Items]
Sales	210	213	193
Int’l \| Operating Segments \| Pharmaceutical segment \| Temodar
Segment Reporting Information [Line Items]
Sales	209	256	268
Int’l \| Operating Segments \| Pharmaceutical segment \| Alliance revenue - Lynparza
Segment Reporting Information [Line Items]
Sales	61	20	0
Int’l \| Operating Segments \| Pharmaceutical segment \| Alliance revenue - Lenvima
Segment Reporting Information [Line Items]
Sales	54	0	0
Int’l \| Operating Segments \| Pharmaceutical segment \| Gardasil/Gardasil 9
Segment Reporting Information [Line Items]
Sales	1,279	743	393
Int’l \| Operating Segments \| Pharmaceutical segment \| ProQuad/M-M-R II/Varivax
Segment Reporting Information [Line Items]
Sales	368	303	279
Int’l \| Operating Segments \| Pharmaceutical segment \| Pneumovax 23
Segment Reporting Information [Line Items]
Sales	281	240	193
Int’l \| Operating Segments \| Pharmaceutical segment \| RotaTeq
Segment Reporting Information [Line Items]
Sales	232	204	169
Int’l \| Operating Segments \| Pharmaceutical segment \| Zostavax
Segment Reporting Information [Line Items]
Sales	195	246	168
Int’l \| Operating Segments \| Pharmaceutical segment \| Bridion
Segment Reporting Information [Line Items]
Sales	531	465	405
Int’l \| Operating Segments \| Pharmaceutical segment \| Noxafil
Segment Reporting Information [Line Items]
Sales	389	327	312
Int’l \| Operating Segments \| Pharmaceutical segment \| Invanz
Segment Reporting Information [Line Items]
Sales	243	241	233
Int’l \| Operating Segments \| Pharmaceutical segment \| Cubicin
Segment Reporting Information [Line Items]
Sales	176	193	181
Int’l \| Operating Segments \| Pharmaceutical segment \| Cancidas
Segment Reporting Information [Line Items]
Sales	314	402	533
Int’l \| Operating Segments \| Pharmaceutical segment \| Primaxin
Segment Reporting Information [Line Items]
Sales	258	270	293
Int’l \| Operating Segments \| Pharmaceutical segment \| Simponi
Segment Reporting Information [Line Items]
Sales	893	819	766
Int’l \| Operating Segments \| Pharmaceutical segment \| Remicade
Segment Reporting Information [Line Items]
Sales	582	837	1,268
Int’l \| Operating Segments \| Pharmaceutical segment \| Belsomra
Segment Reporting Information [Line Items]
Sales	164	112	70
Int’l \| Operating Segments \| Pharmaceutical segment \| Isentress/Isentress HD
Segment Reporting Information [Line Items]
Sales	627	639	666
Int’l \| Operating Segments \| Pharmaceutical segment \| Zepatier
Segment Reporting Information [Line Items]
Sales	447	888	67
Int’l \| Operating Segments \| Pharmaceutical segment \| Zetia
Segment Reporting Information [Line Items]
Sales	813	992	972
Int’l \| Operating Segments \| Pharmaceutical segment \| Vytorin
Segment Reporting Information [Line Items]
Sales	487	627	668
Int’l \| Operating Segments \| Pharmaceutical segment \| Atozet
Segment Reporting Information [Line Items]
Sales	347	225	146
Int’l \| Operating Segments \| Pharmaceutical segment \| Adempas
Segment Reporting Information [Line Items]
Sales	329	300	169
Int’l \| Operating Segments \| Pharmaceutical segment \| Januvia
Segment Reporting Information [Line Items]
Sales	1,718	1,584	1,622
Int’l \| Operating Segments \| Pharmaceutical segment \| Janumet
Segment Reporting Information [Line Items]
Sales	1,417	1,296	1,217
Int’l \| Operating Segments \| Pharmaceutical segment \| NuvaRing
Segment Reporting Information [Line Items]
Sales	180	197	202
Int’l \| Operating Segments \| Pharmaceutical segment \| Implanon/Nexplanon
Segment Reporting Information [Line Items]
Sales	208	191	186
Int’l \| Operating Segments \| Pharmaceutical segment \| Singulair
Segment Reporting Information [Line Items]
Sales	688	692	874
Int’l \| Operating Segments \| Pharmaceutical segment \| Cozaar/Hyzaar
Segment Reporting Information [Line Items]
Sales	431	466	494
Int’l \| Operating Segments \| Pharmaceutical segment \| Nasonex
Segment Reporting Information [Line Items]
Sales	353	333	352
Int’l \| Operating Segments \| Pharmaceutical segment \| Arcoxia
Segment Reporting Information [Line Items]
Sales	335	363	450
Int’l \| Operating Segments \| Pharmaceutical segment \| Follistim AQ
Segment Reporting Information [Line Items]
Sales	153	174	197
Int’l \| Operating Segments \| Pharmaceutical segment \| Dulera
Segment Reporting Information [Line Items]
Sales	28	26	24
Int’l \| Operating Segments \| Pharmaceutical segment \| Fosamax
Segment Reporting Information [Line Items]
Sales	205	235	279
Int’l \| Operating Segments \| Pharmaceutical segment \| Other pharmaceutical
Segment Reporting Information [Line Items]
Sales	2,855	2,917	3,158
Int’l \| Operating Segments \| Animal Health
Segment Reporting Information [Line Items]
Sales	2,974	2,785	2,489
Int’l \| Operating Segments \| Animal Health \| Livestock
Segment Reporting Information [Line Items]
Sales	2,102	2,013	1,841
Int’l \| Operating Segments \| Animal Health \| Companion Animals
Segment Reporting Information [Line Items]
Sales	872	772	648
Int’l \| Operating Segments \| Other segments
Segment Reporting Information [Line Items]
Sales	2	1	0
Int’l \| Other
Segment Reporting Information [Line Items]
Sales	$ 26	$ 376	$ 763

Segment Reporting - Sales of Company's Products (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Segment Reporting Information [Line Items]

Sales

$ 42,294

$ 40,122

$ 39,807

Proceeds from sale of intangible assets

170