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Subsequent Events (Details) - USD ($) $ in Millions | Feb. 07, 2019 | Aug. 03, 2017
--- | --- | ---
Subsequent Event [Line Items] |  |
Additional amount authorized under repurchase program |  | $ 750
Subsequent Event |  |
Subsequent Event [Line Items] |  |
Additional amount authorized under repurchase program | $ 1,000 |

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- Definition Stock Repurchase Program, Additional Amount Authorized to be Repurchased + References No definition available. + Details
Name: | cdw_StockRepurchaseProgramAdditionalAmountAuthorizedtobeRepurchased
Namespace Prefix: | cdw_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |