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Segment Information - Segment Reporting, by Products and Services (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 3,838.6 | $ 4,033.9 | $ 3,994.4 | $ 3,324.7 | $ 3,492.4 | $ 3,708.2 | $ 3,664.6 | $ 3,116.7 | $ 15,191.5 | $ 13,981.9 | $ 12,988.7
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00%
Total Hardware |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 11,941.9 | $ 10,987.6 | $ 10,289.4
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 78.70% | 78.60% | 79.10%
Notebooks/Mobile Devices |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 3,490.9 | $ 2,921.6 | $ 2,537.3
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 23.10% | 20.90% | 19.50%
Netcomm Products |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 2,042.9 | $ 1,958.2 | $ 1,915.0
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 13.40% | 14.00% | 14.70%
Desktops |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 1,159.4 | $ 1,050.0 | $ 965.6
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 7.60% | 7.50% | 7.40%
Video |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 1,076.9 | $ 962.1 | $ 853.8
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 7.10% | 6.90% | 6.60%
Enterprise and Data Storage (Including Drives) |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 1,071.5 | $ 1,053.1 | $ 1,067.2
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 7.10% | 7.50% | 8.20%
Other Hardware |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 3,100.3 | $ 3,042.6 | $ 2,950.5
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 20.40% | 21.80% | 22.70%
Software |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 2,540.1 | $ 2,389.3 | $ 2,152.3
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 16.70% | 17.10% | 16.60%
Services |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 611.3 | $ 575.1 | $ 467.7
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 4.00% | 4.10% | 3.60%
Other |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 98.2 | $ 29.9 | $ 79.3
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 0.60% | 0.20% | 0.70%

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