Segment Information Parentheticals (Details)	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting [Abstract]
Net sales to customers outside of the US, Percent	4.00%	4.00%	4.00%

Net sales to external customers attributed to all foreign countries, in total, in which the company generates revenue, as a percent of total revenues.

No definition available.

Name:	cdw_NetSalesToCustomersOutsideOfUsPercent
Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration