Income Taxes - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Deferred tax liability on unremitted CDW UK earnings	$ 7.0
Unrecognized tax benefits	19.7	$ 19.3	$ 18.7	$ 18.4
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	88.0
State tax credit carryforwards	17.0
Unrecognized tax benefits, impact on effective tax rate, net of tax rate	$ 16.0