Summary of Significant Accounting Policies Valuation Allowances and Reserves (Details) - Allowance for Sales Returns [Member] - USD ($) $ in Millions |
12 Months Ended | ||
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Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Movement in Valuation Allowances and Reserves [Roll Forward] | |||
| Balance beginning of year | $ 93 | $ 103 | $ 109 |
| Additions- charged to earnings | 982 | 1,010 | 1,213 |
| Deductions | (979) | (1,020) | (1,219) |
| Balance end of year | $ 96 | $ 93 | $ 103 |
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
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- Definition Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of increase in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from charges to costs and expenses. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Total of the deductions in a given period to allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, representing receivables written off as uncollectible and portions of the reserves utilized, respectively. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Details
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