Acquisition Fair Value of Consideration Transferred (Details) - Kelway TopCo Limited [Member] $ in Millions	Aug. 01, 2015 USD ($)
Business Acquisition [Line Items]
Cash	$ 291.6
Fair value of CDW common stock	33.2
Fair value of previously held equity investment on the date of acquisition	174.9
Total consideration	$ 499.7

Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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