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Segment Information - Products and Services (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 4,074.8 | $ 4,373.2 | $ 4,186.1 | $ 3,606.4 | $ 3,752.1 | $ 3,933.2 | $ 3,891.7 | $ 3,256.0 | $ 16,240.5 | $ 14,832.9 | $ 13,672.7
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 100.00% | 100.00% | 100.00%
Total Hardware |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 13,082.4 | $ 11,960.4 | $ 10,916.0
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 80.60% | 80.60% | 79.80%
Notebooks/Mobile Devices |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 4,053.6 | $ 3,519.8 | $ 2,942.9
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 25.00% | 23.70% | 21.50%
Netcomm Products |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 2,119.8 | $ 2,040.3 | $ 1,957.0
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 13.10% | 13.80% | 14.30%
Desktops |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 1,318.2 | $ 1,207.0 | $ 1,087.7
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 8.10% | 8.10% | 8.00%
Video |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 1,185.6 | $ 1,078.4 | $ 963.0
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 7.30% | 7.30% | 7.00%
Enterprise and Data Storage (Including Drives) |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 1,099.2 | $ 1,087.3 | $ 1,073.9
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 6.80% | 7.30% | 7.90%
Other Hardware |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 3,306.0 | $ 3,027.6 | $ 2,891.5
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 20.30% | 20.40% | 21.10%
Software |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 2,347.0 | $ 2,156.9 | $ 2,072.3
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 14.40% | 14.50% | 15.20%
Services |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 697.3 | $ 602.7 | $ 564.2
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 4.30% | 4.10% | 4.10%
Other |  |  |  |  |  |  |  |  |  |  |
Net Sales from External Customer [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 113.8 | $ 112.9 | $ 120.2
Percentage of Total Net Sales |  |  |  |  |  |  |  |  | 0.70% | 0.80% | 0.90%

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