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Income Taxes - Narrative (Details) $ in Millions | 3 Months Ended | 12 Months Ended
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Dec. 31, 2018 USD ($) | Dec. 31, 2018 USD ($)
Operating Loss Carryforwards [Line Items] |  |
Provisional amount, tax benefit | $ 2 |
Deferred income tax expense related to basis difference in CDW UK |  | $ 19
Deferred tax liability on unremitted CDW UK earnings |  | 3
Unrecognized tax benefits that would impact effective tax rate | 15 | 15
Unrecognized tax benefits that would impact effective tax rate, net of tax rate | 12 | 12
State and Local Jurisdiction |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 11 | 11
State tax credit carryforwards | $ 25 | $ 25

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- Definition Deferred Tax Liability on Unremitted Foreign Earnings + References No definition available. + Details
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- Definition Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) + References No definition available. + Details
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- Definition Unrecognized Tax Benefits that Would Impact Effective Tax Rate, Net of Tax Rate + References No definition available. + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
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- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
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