v2.4.1.9

Segment Information Segment Reporting, by Products and Services (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Net Sales from External Customer [Line Items]
Net sales to customers outside of the US, Percent									4.00%cdw_NetSalesToCustomersOutsideOfUsPercent		4.00%cdw_NetSalesToCustomersOutsideOfUsPercent		4.00%cdw_NetSalesToCustomersOutsideOfUsPercent
Revenue, Net	$ 3,050,100,000us-gaap_SalesRevenueNet	$ 3,266,100,000us-gaap_SalesRevenueNet	$ 3,106,000,000us-gaap_SalesRevenueNet	$ 2,652,300,000us-gaap_SalesRevenueNet	$ 2,713,300,000us-gaap_SalesRevenueNet	$ 2,864,300,000us-gaap_SalesRevenueNet	$ 2,779,300,000us-gaap_SalesRevenueNet	$ 2,411,700,000us-gaap_SalesRevenueNet	$ 12,074,500,000us-gaap_SalesRevenueNet		$ 10,768,600,000us-gaap_SalesRevenueNet		$ 10,128,200,000us-gaap_SalesRevenueNet
Revenue net, by Product and Service, Percentage									100.00%cdw_RevenuenetbyProductandServicePercentage		100.00%cdw_RevenuenetbyProductandServicePercentage		100.00%cdw_RevenuenetbyProductandServicePercentage
Long-Lived Assets in Foreign Countries, Percent	1.00%cdw_LongLivedAssetsInForeignCountriesPercent				1.00%cdw_LongLivedAssetsInForeignCountriesPercent				1.00%cdw_LongLivedAssetsInForeignCountriesPercent		1.00%cdw_LongLivedAssetsInForeignCountriesPercent
Notebooks/Mobile Devices [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									2,352,300,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_NotebooksMobileDevicesMember		1,698,400,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_NotebooksMobileDevicesMember		1,462,800,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_NotebooksMobileDevicesMember
Revenue net, by Product and Service, Percentage									19.50%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_NotebooksMobileDevicesMember		15.80%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_NotebooksMobileDevicesMember		14.40%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_NotebooksMobileDevicesMember
NetComm Products [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									1,615,900,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_NetcommProductsMember		1,486,300,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_NetcommProductsMember		1,351,500,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_NetcommProductsMember
Revenue net, by Product and Service, Percentage									13.40%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_NetcommProductsMember		13.80%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_NetcommProductsMember		13.30%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_NetcommProductsMember
Enterprise and Data Storage (Including Drives) [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									1,024,300,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_EnterpriseAndDataStorageIncludingDrivesMember		999,200,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_EnterpriseAndDataStorageIncludingDrivesMember		981,500,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_EnterpriseAndDataStorageIncludingDrivesMember
Revenue net, by Product and Service, Percentage									8.50%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_EnterpriseAndDataStorageIncludingDrivesMember		9.30%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_EnterpriseAndDataStorageIncludingDrivesMember		9.70%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_EnterpriseAndDataStorageIncludingDrivesMember
Other Hardware [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									4,549,200,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_OtherHardwareMember		4,178,500,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_OtherHardwareMember		4,075,700,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_OtherHardwareMember
Revenue net, by Product and Service, Percentage									37.60%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_OtherHardwareMember		38.80%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_OtherHardwareMember		40.30%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_OtherHardwareMember
Software [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									2,076,700,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_SoftwareProductsMember		1,993,100,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_SoftwareProductsMember		1,877,700,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_SoftwareProductsMember
Revenue net, by Product and Service, Percentage									17.20%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_SoftwareProductsMember		18.50%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_SoftwareProductsMember		18.50%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_SoftwareProductsMember
Services [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									371,400,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_ServicesMember		332,700,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_ServicesMember		285,000,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_ServicesMember
Revenue net, by Product and Service, Percentage									3.10%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_ServicesMember		3.10%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_ServicesMember		2.80%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_ServicesMember
Other [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									84,700,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_OtherProductsAndServicesMember	[1]	80,400,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_OtherProductsAndServicesMember	[1]	94,000,000us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = cdw_OtherProductsAndServicesMember	[1]
Revenue net, by Product and Service, Percentage									0.70%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_OtherProductsAndServicesMember	[1]	0.70%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_OtherProductsAndServicesMember	[1]	1.00%cdw_RevenuenetbyProductandServicePercentage / us-gaap_ProductOrServiceAxis = cdw_OtherProductsAndServicesMember	[1]
Public [Member]
Net Sales from External Customer [Line Items]
Revenue, Net	1,169,100,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember	1,468,800,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember	1,271,600,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember	969,900,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember	990,500,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember	1,244,600,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember	1,082,600,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember	846,800,000us-gaap_SalesRevenueNet / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember
Federal [Member] | Public [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									$ 884,200,000us-gaap_SalesRevenueNet / cdw_PublicAxis = cdw_FederalMember / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember		$ 764,400,000us-gaap_SalesRevenueNet / cdw_PublicAxis = cdw_FederalMember / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember		$ 964,700,000us-gaap_SalesRevenueNet / cdw_PublicAxis = cdw_FederalMember / us-gaap_StatementBusinessSegmentsAxis = cdw_PublicMember
[1] Includes items such as delivery charges to customers and certain commission revenue.

X

- Definition

Amount of long-lived assets located in foreign countries in total, in which the entity holds assets, as a percentage of total long-lived assets.

+ References

No definition available.

+ Details

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Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

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

+ References

No definition available.

+ Details

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

X

- Definition

Revenue net, by Product and Service, Percentage

+ References

No definition available.

+ Details

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

X

- Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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X

- Details

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Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=cdw_NetcommProductsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=cdw_NotebooksMobileDevicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=cdw_OtherHardwareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=cdw_OtherProductsAndServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=cdw_ServicesMember
Namespace Prefix:
Data Type:	na
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Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=cdw_SoftwareProductsMember
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X

- Details

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