Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Net sales	$ 21,376.0	$ 23,748.7	$ 20,820.8
Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,960.8	10,350.1	8,179.7
Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,556.0	1,938.9	1,870.1
Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	8,305.7	8,551.3	8,183.6
Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	2,553.5	2,908.4	2,587.4
Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	18,512.9	21,016.1	18,990.0
Transferred at a point in time where CDW is principal | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	7,515.7	8,971.4	7,332.3
Transferred at a point in time where CDW is principal | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,374.1	1,751.1	1,734.7
Transferred at a point in time where CDW is principal | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	7,411.1	7,717.1	7,634.3
Transferred at a point in time where CDW is principal | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	2,212.0	2,576.5	2,288.7
Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Net sales	1,521.8	1,414.0	1,049.6
Transferred at a point in time where CDW is agent | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	778.0	749.3	517.5
Transferred at a point in time where CDW is agent | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	145.3	140.1	112.3
Transferred at a point in time where CDW is agent | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	480.6	426.9	336.6
Transferred at a point in time where CDW is agent | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	117.9	97.7	83.2
Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	1,341.3	1,318.6	781.2
Transferred over time where CDW is principal | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	667.1	629.4	329.9
Transferred over time where CDW is principal | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	36.6	47.7	23.1
Transferred over time where CDW is principal | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	414.0	407.3	212.7
Transferred over time where CDW is principal | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	223.6	234.2	215.5
Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,960.8	10,350.1	8,179.7
Corporate | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,960.8	10,350.1	8,179.7
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	1,556.0	1,938.9	1,870.1
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	1,556.0	1,938.9	1,870.1
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	2,669.1	2,574.3	2,155.6
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	2,669.1	2,574.3	2,155.6
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	3,298.3	3,621.4	4,108.7
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	3,298.3	3,621.4	4,108.7
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	2,338.3	2,355.6	1,919.3
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	2,338.3	2,355.6	1,919.3
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	2,553.5	2,908.4	2,587.4
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	2,553.5	2,908.4	2,587.4
Hardware
Disaggregation of Revenue [Line Items]
Net sales	15,702.6	18,091.0	16,769.6
Hardware | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	6,216.9	7,561.0	6,427.9
Hardware | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,242.3	1,610.7	1,587.9
Hardware | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	6,460.4	6,763.9	6,827.1
Hardware | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	1,783.0	2,155.4	1,926.7
Software
Disaggregation of Revenue [Line Items]
Net sales	3,799.3	3,684.9	2,802.4
Software | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	1,772.3	1,781.5	1,172.4
Software | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	232.8	232.9	211.0
Software | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	1,295.4	1,196.9	1,017.3
Software | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	498.8	473.6	401.7
Services
Disaggregation of Revenue [Line Items]
Net sales	1,761.3	1,842.0	1,126.1
Services | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	909.1	929.3	510.1
Services | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	62.6	73.8	49.1
Services | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	531.5	570.7	321.5
Services | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	258.1	268.2	245.4
Other
Disaggregation of Revenue [Line Items]
Net sales	112.8	130.8	122.7
Other | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	62.5	78.3	69.3
Other | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	18.3	21.5	22.1
Other | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	18.4	19.8	17.7
Other | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	13.6	11.2	13.6
United States
Disaggregation of Revenue [Line Items]
Net sales	18,754.9	20,828.6	18,238.8
United States | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	8,894.5	10,321.2	8,165.4
United States | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	1,534.5	1,934.8	1,870.1
United States | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	8,299.4	8,550.8	8,183.6
United States | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	26.5	21.8	19.7
Rest of World
Disaggregation of Revenue [Line Items]
Net sales	2,621.1	2,920.1	2,582.0
Rest of World | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	66.3	28.9	14.3
Rest of World | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	21.5	4.1	0.0
Rest of World | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	6.3	0.5	0.0
Rest of World | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	$ 2,527.0	$ 2,886.6	$ 2,567.7