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Related Party Transactions - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Nov. 30, 2015 | Aug. 18, 2015 | May 22, 2015 | Dec. 31, 2015 | Aug. 01, 2015
Related Party Transaction [Line Items] |  |  |  |  |
Shares sold by certain selling stockholders (in shares) | 9.2 | 12.9 | 11.5 |  |
Repurchases of common stock (in shares) | 1.0 | 2.3 | 2.0 |  |
Share repurchase transaction (in dollars per share) |  |  | $ 36.60 |  |
Over-Allotment Option |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Shares sold by certain selling stockholders (in shares) | 1.2 | 1.7 | 1.5 |  |
CDW UK |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Non-controlling interest held |  |  |  |  | 35.00%
Percent of outstanding common stock purchased |  |  |  |  | 65.00%
Net sales from related parties |  |  |  | $ 10 |

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