v2.4.1.9

Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 01, 2014	Aug. 05, 2014	Mar. 20, 2014
Related Party Transaction [Line Items]
Management Fee	$ 0us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty	$ 2.5us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty	$ 5.0us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Net proceeds used for termination of Management Services Agreement		24.4cdw_NetproceedsusedforterminationofManagementServicesAgreement
Senior notes due 2019 [Member]
Related Party Transaction [Line Items]
Debt Instrument, Repurchased Face Amount				$ 541.4us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = cdw_SeniorNotesDue2019Member	$ 234.7us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = cdw_SeniorNotesDue2019Member	$ 25.0us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = cdw_SeniorNotesDue2019Member

X

- Definition

Net proceeds used for termination of Management Services Agreement

+ References

No definition available.

+ Details

Name:	cdw_NetproceedsusedforterminationofManagementServicesAgreement
Namespace Prefix:	cdw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentRepurchasedFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

Name:	us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

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

X

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesDue2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: