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Summary of Accounting Policies - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2019 | Jan. 01, 2018
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Product return period and expiration | 12 months |  |  |  |
Customer discounts | $ 10,700 | $ 10,700 | $ 9,700 |  |
Accrual for chargebacks reflected as direct reduction to accounts receivable | 245 | 198 |  |  |
Accrual for rebates included in accrued and other current liabilities | 2,400 | 2,400 |  |  |
Depreciation | 1,400 | 1,500 | 1,600 |  |
Advertising and promotion costs | 2,100 | 2,200 | 2,100 |  |
Decrease in deferred income taxes | (1,702) | (2,219) |  |  |
Accumulated other comprehensive loss | 5,545 | 4,910 |  |  |
Net periodic defined benefit plan (credit) cost other than service cost | (512) | (512) | $ (531) |  |
ASU 2016-01 (Financial Instruments) |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Increase (decrease) in retained earnings | 8 |  |  |  |
Accumulated other comprehensive loss |  |  |  |  | $ 8
ASU 2016-16 (Intra-Entity Transfers Other than Inventory) |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Increase (decrease) in retained earnings | 54 |  |  |  |
Decrease in deferred income taxes | 54 |  |  |  | 54
Accounting Standards Update 2017-12 |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Increase (decrease) in retained earnings | (11) |  |  |  |
Accounting Standard Update 2018-02 |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Accumulated other comprehensive loss |  |  |  |  | $ 266
Enterprise wide resource planning system |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Unamortized capitalized software costs | 439 | $ 449 |  |  |
Difference between Revenue Guidance in Effect before and after Topic 606 | ASU 2014-09 (Revenue) |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Increase (decrease) in retained earnings | $ 5 |  |  |  |
Minimum |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Product return period | 3 months |  |  |  |
Estimated useful life of intangible assets | 2 years |  |  |  |
Minimum | Enterprise wide resource planning system |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of intangible assets | 6 years |  |  |  |
Minimum | Capitalized Software |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of intangible assets | 3 years |  |  |  |
Minimum | Buildings |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of property, plant and equipment | 25 years |  |  |  |
Minimum | Machinery, equipment and office furnishings |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of property, plant and equipment | 3 years |  |  |  |
Minimum | United States | Pharmaceutical segment |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Payment terms | 36 days |  |  |  |
Minimum | United States | Animal Health |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Payment terms | 30 days |  |  |  |
Minimum | Outside of the United States |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Payment terms | 30 days |  |  |  |
Maximum |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Product return period | 6 months |  |  |  |
Estimated useful life of intangible assets | 20 years |  |  |  |
Maximum | Enterprise wide resource planning system |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of intangible assets | 10 years |  |  |  |
Maximum | Capitalized Software |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of intangible assets | 5 years |  |  |  |
Maximum | Buildings |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of property, plant and equipment | 45 years |  |  |  |
Maximum | Machinery, equipment and office furnishings |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful life of property, plant and equipment | 15 years |  |  |  |
Maximum | United States | Animal Health |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Payment terms | 90 days |  |  |  |
Maximum | Outside of the United States |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Payment terms | 90 days |  |  |  |
Subsequent Event | Accounting Standards Update 2016-02 |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Operating lease, right-of-use assets |  |  |  | $ 1,000 |
Operating lease, liability |  |  |  | $ 1,000 |

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