Segment Reporting - Reconciliation of Segment Profits to Income Before Taxes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Profits	$ 2,086	$ 2,439	$ 3,432	$ 4,442
Interest income	81	96	165	194
Interest expense	(194)	(193)	(379)	(375)
Equity income from affiliates	64	5	12	(8)
Depreciation and amortization			(2,363)	(2,355)
Research and development	(2,274)	(1,782)	(5,470)	(3,612)
Restructuring costs	(228)	(166)	(323)	(317)
Total segment profits
Segment Reporting Information [Line Items]
Profits	6,302	6,096	12,582	11,707
Total segment profits \| Pharmaceutical segment
Segment Reporting Information [Line Items]
Profits	5,826	5,590	11,630	10,751
Total segment profits \| Animal Health segment
Segment Reporting Information [Line Items]
Profits	450	395	864	812
Total segment profits \| Other segments
Segment Reporting Information [Line Items]
Profits	26	111	88	144
Other profits
Segment Reporting Information [Line Items]
Profits	(2)	43	(89)	186
Unallocated
Segment Reporting Information [Line Items]
Interest income	81	96	165	194
Interest expense	(194)	(193)	(379)	(375)
Equity income from affiliates	66	5	16	(7)
Depreciation and amortization	(332)	(332)	(682)	(702)
Research and development	(2,041)	(1,560)	(5,023)	(3,191)
Amortization of purchase accounting adjustments	(732)	(779)	(1,464)	(1,557)
Restructuring costs	(228)	(166)	(323)	(317)
Other unallocated, net	$ (834)	$ (771)	$ (1,371)	$ (1,496)

Amortization of purchase accounting adjustments.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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