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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Billions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Disaggregation of Revenue [Line Items] |  |
Sales discounts for products | $ 2.4 | $ 2.5
Return period after expiration date of product | 12 months |
Minimum |  |
Disaggregation of Revenue [Line Items] |  |
Return period prior to expiration date of product | 3 months |
Minimum | United States |  |
Disaggregation of Revenue [Line Items] |  |
Payment terms | 36 days |
Minimum | Outside of the United States |  |
Disaggregation of Revenue [Line Items] |  |
Payment terms | 30 days |
Maximum |  |
Disaggregation of Revenue [Line Items] |  |
Return period prior to expiration date of product | 6 months |
Maximum | United States |  |
Disaggregation of Revenue [Line Items] |  |
Payment terms | 90 days |
Maximum | Outside of the United States |  |
Disaggregation of Revenue [Line Items] |  |
Payment terms | 90 days |

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- Definition Aggregate cash discounts given by the entity for goods sold to customers including, but not limited to, early payments of accounts due. For example, selling terms of "2/10, net 30" entitle a customer to a 2% discount for prompt payment within 10 days, otherwise full payment is expected in 30 days. Discounts are a deduction from gross revenue in arriving at net revenue. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1(a)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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