v2.4.1.9

Long-Term Debt Term Loan (Details) (USD $)	12 Months Ended				1 Months Ended		9 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Jul. 31, 2013	Apr. 30, 2013	Sep. 30, 2013	Apr. 29, 2013	Mar. 31, 2015
Debt Instrument [Line Items]
Proceeds from issuance of long-term debt	$ 1,175,000,000us-gaap_ProceedsFromIssuanceOfLongTermDebt		$ 1,535,200,000us-gaap_ProceedsFromIssuanceOfLongTermDebt	$ 135,700,000us-gaap_ProceedsFromIssuanceOfLongTermDebt
Deferred financing costs, net	33,000,000us-gaap_DeferredFinanceCostsNoncurrentNet		30,100,000us-gaap_DeferredFinanceCostsNoncurrentNet	53,200,000us-gaap_DeferredFinanceCostsNoncurrentNet
Debt, long-term and short-term	3,192,400,000us-gaap_DebtInstrumentCarryingAmount
Gains (Losses) on Extinguishment of Debt	90,700,000us-gaap_GainsLossesOnExtinguishmentOfDebt		64,000,000us-gaap_GainsLossesOnExtinguishmentOfDebt	17,200,000us-gaap_GainsLossesOnExtinguishmentOfDebt
Write off of Deferred Debt Issuance Cost	12,600,000us-gaap_WriteOffOfDeferredDebtIssuanceCost		20,100,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Fee on Unused Portion, Basis Points	25cdw_LineOfCreditFacilityFeeOnUnusedPortionBasisPoints / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Deferred financing costs, net	6,400,000us-gaap_DeferredFinanceCostsNoncurrentNet / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Debt, long-term and short-term	0us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember		0us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Long-term Debt, Weighted Average Interest Rate	0.00%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember	[1]
Gains (Losses) on Extinguishment of Debt	400,000us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember
Term Loan [Member]
Debt Instrument [Line Items]
Proceeds from issuance of long-term debt						1,350,000,000us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Discount, percent of par					99.25%cdw_DiscountPercentOfPar / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember			99.75%cdw_DiscountPercentOfPar / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Debt Instrument, Unamortized Discount	(3,700,000)us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember		(4,400,000)us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember		1,400,000us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember			3,400,000us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Deferred Finance Costs, Net					6,100,000us-gaap_DeferredFinanceCostsNet / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Debt, long-term and short-term	1,513,500,000us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember		1,528,900,000us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Long-term Debt, Weighted Average Interest Rate	3.25%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember	[1]
Gains (Losses) on Extinguishment of Debt			10,300,000us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Debt Instrument, Face Amount					190,000,000us-gaap_ProceedsFromIssuanceOfDebt / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Net leverage ratio	3.1cdw_NetLeverageRatio / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Quarterly amortization payment of original principal, Percent	0.25%cdw_QuarterlyAmortizationPaymentOfOriginalPrincipalPercent / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Term Loan [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	3.25%us-gaap_LongtermDebtWeightedAverageInterestRate / cdw_InterestRateBasisAxis = cdw_LiborMember / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember
Prior Term Loan Facility [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term								1,299,500,000us-gaap_DebtInstrumentCarryingAmount / us-gaap_LongtermDebtTypeAxis = cdw_PriorTermLoanFacilityMember
Term Loan, Repayments							40,000,000us-gaap_RepaymentsOfDebt / us-gaap_LongtermDebtTypeAxis = cdw_PriorTermLoanFacilityMember
Minimum [Member] | Revolving Credit Facility [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	0.50%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_AbrMember / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Minimum [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.50%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_LiborMember / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Minimum [Member] | Term Loan [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.25%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_AbrMember / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Minimum [Member] | Term Loan [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.25%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_LiborMember / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Reference Interest Rate Floor	1.00%cdw_ReferenceInterestRateFloor / cdw_InterestRateBasisAxis = cdw_LiborMember / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Maximum [Member] | Revolving Credit Facility [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.00%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_AbrMember / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Maximum [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.00%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_LiborMember / us-gaap_LongtermDebtTypeAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Maximum [Member] | Term Loan [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.50%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_AbrMember / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Maximum [Member] | Term Loan [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.50%cdw_VariableInterestRateMargin / cdw_InterestRateBasisAxis = cdw_LiborMember / us-gaap_LongtermDebtTypeAxis = cdw_TermLoanMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Cap agreement effective January 14, 2013-2015 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount	1,150,000,000invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = cdw_CapAgreementEffectiveJanuary1420132015Member
Derivative, Cap Interest Rate	2.40%us-gaap_DerivativeCapInterestRate / us-gaap_DerivativeByNatureAxis = cdw_CapAgreementEffectiveJanuary1420132015Member
Derivative Asset, Noncurrent	0us-gaap_DerivativeAssetsNoncurrent / us-gaap_DerivativeByNatureAxis = cdw_CapAgreementEffectiveJanuary1420132015Member
Cap agreement effective January 14, 2015-2017 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount	1,000,000,000invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member
Derivative Asset, Noncurrent	1,700,000us-gaap_DerivativeAssetsNoncurrent / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member
Subsequent Event [Member] | Cap agreement effective January 14, 2015-2017 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount									$ 400,000,000invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Derivative, Cap Interest Rate									2.00%us-gaap_DerivativeCapInterestRate / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
[1] Interest rate at December 31, 2014.

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