Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Net sales	$ 20,998.7	$ 21,376.0	$ 23,748.7
Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,837.2	8,960.8	10,350.1
Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,523.5	1,556.0	1,938.9
Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	8,157.7	8,305.7	8,551.3
Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	2,480.3	2,553.5	2,908.4
Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	17,973.0	18,512.9	21,016.1
Transferred at a point in time where CDW is principal | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	7,369.0	7,515.7	8,971.4
Transferred at a point in time where CDW is principal | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,325.6	1,374.1	1,751.1
Transferred at a point in time where CDW is principal | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	7,176.7	7,411.1	7,717.1
Transferred at a point in time where CDW is principal | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	2,101.7	2,212.0	2,576.5
Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Net sales	1,607.6	1,521.8	1,414.0
Transferred at a point in time where CDW is agent | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	807.1	778.0	749.3
Transferred at a point in time where CDW is agent | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	146.7	145.3	140.1
Transferred at a point in time where CDW is agent | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	526.9	480.6	426.9
Transferred at a point in time where CDW is agent | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	126.9	117.9	97.7
Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	1,418.1	1,341.3	1,318.6
Transferred over time where CDW is principal | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	661.1	667.1	629.4
Transferred over time where CDW is principal | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	51.2	36.6	47.7
Transferred over time where CDW is principal | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	454.1	414.0	407.3
Transferred over time where CDW is principal | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	251.7	223.6	234.2
Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,837.2	8,960.8	10,350.1
Corporate | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,837.2	8,960.8	10,350.1
Corporate | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Corporate | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Corporate | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,523.5	1,556.0	1,938.9
Small Business | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Small Business | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,523.5	1,556.0	1,938.9
Small Business | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Small Business | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Government
Disaggregation of Revenue [Line Items]
Net sales	2,486.9	2,669.1	2,574.3
Government | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Government | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Government | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	2,486.9	2,669.1	2,574.3
Government | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Education
Disaggregation of Revenue [Line Items]
Net sales	3,167.3	3,298.3	3,621.4
Education | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Education | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Education | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	3,167.3	3,298.3	3,621.4
Education | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Healthcare
Disaggregation of Revenue [Line Items]
Net sales	2,503.5	2,338.3	2,355.6
Healthcare | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Healthcare | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Healthcare | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	2,503.5	2,338.3	2,355.6
Healthcare | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Other
Disaggregation of Revenue [Line Items]
Net sales	2,480.3	2,553.5	2,908.4
Other | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Other | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Other | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	0.0	0.0	0.0
Other | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	2,480.3	2,553.5	2,908.4
Hardware
Disaggregation of Revenue [Line Items]
Net sales	15,219.1	15,702.6	18,091.0
Hardware | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	6,015.5	6,216.9	7,561.0
Hardware | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,201.6	1,242.3	1,610.7
Hardware | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	6,225.1	6,460.4	6,763.9
Hardware | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	1,776.9	1,783.0	2,155.4
Software
Disaggregation of Revenue [Line Items]
Net sales	3,804.4	3,799.3	3,684.9
Software | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	1,863.0	1,772.3	1,781.5
Software | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	228.7	232.8	232.9
Software | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	1,320.5	1,295.4	1,196.9
Software | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	392.2	498.8	473.6
Services
Disaggregation of Revenue [Line Items]
Net sales	1,867.3	1,761.3	1,842.0
Services | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	898.5	909.1	929.3
Services | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	75.8	62.6	73.8
Services | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	593.6	531.5	570.7
Services | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	299.4	258.1	268.2
Other
Disaggregation of Revenue [Line Items]
Net sales	107.9	112.8	130.8
Other | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	60.2	62.5	78.3
Other | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	17.4	18.3	21.5
Other | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	18.5	18.4	19.8
Other | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	11.8	13.6	11.2
United States
Disaggregation of Revenue [Line Items]
Net sales	18,456.9	18,754.9	20,828.6
United States | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,779.4	8,894.5	10,321.2
United States | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,499.8	1,534.5	1,934.8
United States | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	8,150.4	8,299.4	8,550.8
United States | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	27.3	26.5	21.8
Rest of World
Disaggregation of Revenue [Line Items]
Net sales	2,541.8	2,621.1	2,920.1
Rest of World | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	57.8	66.3	28.9
Rest of World | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	23.7	21.5	4.1
Rest of World | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	7.3	6.3	0.5
Rest of World | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	$ 2,453.0	$ 2,527.0	$ 2,886.6