Income Taxes	3 Months Ended
Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax expense was $39 million for the three months ended March 31, 2019 and 2018. The effective income tax rate, expressed by calculating the income tax expense as a percentage of Income before income taxes, was 20.2% for the three months ended March 31, 2019 and differed from the US federal statutory rate of 21.0% primarily due to excess tax benefits on equity-based compensation and a discrete tax benefit of $3 million related to CDW Canada's acquisition of Scalar, partially offset by state and local income taxes. The effective tax rate for the same period of the prior year was 23.4% and differed from the US federal statutory rate of 21.0% primarily due to state and local income taxes partially offset by excess tax benefits on equity-based compensation.

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI http://asc.fasb.org/topic&trid=2144680

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