Segment Reporting - Reconciliation of Segment Profits to Income Before Taxes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Profits	$ 2,665	$ 200	$ 6,097	$ 4,642
Interest income	92	90	257	284
Interest expense	(190)	(189)	(569)	(564)
Equity income from affiliates	81	18	93	11
Depreciation and amortization			(3,424)	(3,509)
Research and development	(2,068)	(4,413)	(7,538)	(8,024)
Restructuring costs	(171)	(153)	(494)	(470)
Aggregate charge related to termination of collaboration agreement with Samsung			420	0
Total segment profits
Segment Reporting Information [Line Items]
Profits	6,893	6,388	19,476	18,093
Total segment profits \| Pharmaceutical segment
Segment Reporting Information [Line Items]
Profits	6,479	5,906	18,109	16,657
Total segment profits \| Animal Health segment
Segment Reporting Information [Line Items]
Profits	409	389	1,273	1,202
Total segment profits \| Other segments
Segment Reporting Information [Line Items]
Profits	5	93	94	234
Other profits (losses)
Segment Reporting Information [Line Items]
Profits	55	(78)	(35)	107
Unallocated
Segment Reporting Information [Line Items]
Interest income	92	90	257	284
Interest expense	(190)	(189)	(569)	(564)
Equity income from affiliates	85	23	101	16
Depreciation and amortization	(324)	(334)	(1,006)	(1,036)
Research and development	(1,855)	(4,208)	(6,878)	(7,399)
Amortization of purchase accounting adjustments	(679)	(765)	(2,144)	(2,322)
Restructuring costs	(171)	(153)	(494)	(470)
Aggregate charge related to termination of collaboration agreement with Samsung	(420)	0	(420)	0
Other unallocated, net	$ (821)	$ (574)	$ (2,191)	$ (2,067)

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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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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