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v3.19.3.a.u2

Description of Business and Summary of Significant Accounting Policies - Additional Information (Details) | 12 Months Ended
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Dec. 31, 2019 subsidiary
Accounting Policies [Abstract] |
Number of owned subsidiaries | 2
Years forecasted in goodwill impairment income approach | 5 years

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- Definition Forecasted Years for Goodwill Impairment + References No definition available. + Details
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Period Type: | duration

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- Definition Number of Owned Subsidiaries + References No definition available. + Details
Name: | cdw_NumberofOwnedSubsidiaries
Namespace Prefix: | cdw_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
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Period Type: | duration