Segment Information - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Total Net sales	$ 5,737.4	$ 5,516.6	$ 16,913.1	$ 15,812.7
Percentage of Total Net Sales	100.00%	100.00%	100.00%	100.00%
Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	$ 4,867.5	$ 4,721.0	$ 14,446.5	$ 13,561.6
Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	452.3	428.1	1,270.9	1,194.1
Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	417.6	367.5	1,195.7	1,057.0
Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	2,255.4	2,161.2	7,072.9	6,492.3
Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	433.8	379.7	1,269.7	1,143.5
Government
Disaggregation of Revenue [Line Items]
Total Net sales	744.7	691.0	1,939.0	1,873.4
Education
Disaggregation of Revenue [Line Items]
Total Net sales	911.2	995.7	2,470.3	2,609.9
Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	693.9	649.0	2,110.3	1,820.4
Other
Disaggregation of Revenue [Line Items]
Total Net sales	698.4	640.0	2,050.9	1,873.2
Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	$ 4,088.5	$ 3,958.6	$ 12,274.8	$ 11,566.6
Percentage of Total Net Sales	71.30%	71.80%	72.50%	73.10%
Software
Disaggregation of Revenue [Line Items]
Total Net sales	$ 1,093.6	$ 1,048.3	$ 3,032.1	$ 2,778.3
Percentage of Total Net Sales	19.10%	19.00%	17.90%	17.60%
Services
Disaggregation of Revenue [Line Items]
Total Net sales	$ 525.6	$ 481.9	$ 1,520.1	$ 1,386.1
Percentage of Total Net Sales	9.20%	8.70%	9.00%	8.80%
Other
Disaggregation of Revenue [Line Items]
Total Net sales	$ 29.7	$ 27.8	$ 86.1	$ 81.7
Percentage of Total Net Sales	0.40%	0.50%	0.60%	0.50%
Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	$ 2,255.4	$ 2,161.2	$ 7,072.9	$ 6,492.3
Corporate \| Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	1,884.2	1,799.8	5,928.4	5,409.5
Corporate \| Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	198.9	197.5	616.3	585.5
Corporate \| Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	172.3	163.9	528.2	497.3
Corporate \| Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	2,255.4	2,161.2	7,072.9	6,492.3
Corporate \| Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate \| Government
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate \| Education
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate \| Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate \| Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	1,521.8	1,468.6	4,875.6	4,466.4
Corporate \| Software
Disaggregation of Revenue [Line Items]
Total Net sales	492.8	458.4	1,460.7	1,312.1
Corporate \| Services
Disaggregation of Revenue [Line Items]
Total Net sales	224.9	218.9	689.5	668.1
Corporate \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	15.9	15.3	47.1	45.7
Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	433.8	379.7	1,269.7	1,143.5
Small Business \| Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	373.6	328.1	1,106.5	997.0
Small Business \| Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	44.6	37.0	116.1	110.3
Small Business \| Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	15.6	14.6	47.1	36.2
Small Business \| Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business \| Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	433.8	379.7	1,269.7	1,143.5
Small Business \| Government
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business \| Education
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business \| Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business \| Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	332.8	294.7	994.4	902.0
Small Business \| Software
Disaggregation of Revenue [Line Items]
Total Net sales	73.8	60.3	195.8	173.7
Small Business \| Services
Disaggregation of Revenue [Line Items]
Total Net sales	22.4	20.4	65.8	54.7
Small Business \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	4.8	4.3	13.7	13.1
Public
Disaggregation of Revenue [Line Items]
Total Net sales	2,349.8	2,335.7	6,519.6	6,303.7
Public \| Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	2,022.1	2,053.4	5,689.3	5,561.3
Public \| Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	170.9	160.0	417.0	402.7
Public \| Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	156.8	122.3	413.3	339.7
Public \| Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Public \| Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Public \| Government
Disaggregation of Revenue [Line Items]
Total Net sales	744.7	691.0	1,939.0	1,873.4
Public \| Education
Disaggregation of Revenue [Line Items]
Total Net sales	911.2	995.7	2,470.3	2,609.9
Public \| Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	693.9	649.0	2,110.3	1,820.4
Public \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Public \| Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	1,714.2	1,742.8	4,903.2	4,855.4
Public \| Software
Disaggregation of Revenue [Line Items]
Total Net sales	435.1	427.0	1,079.5	992.6
Public \| Services
Disaggregation of Revenue [Line Items]
Total Net sales	195.1	161.0	522.7	441.6
Public \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	5.4	4.9	14.2	14.1
Other
Disaggregation of Revenue [Line Items]
Total Net sales	698.4	640.0	2,050.9	1,873.2
Other \| Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	587.6	539.7	1,722.3	1,593.8
Other \| Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	37.9	33.6	121.5	95.6
Other \| Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	72.9	66.7	207.1	183.8
Other \| Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other \| Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other \| Government
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other \| Education
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other \| Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	698.4	640.0	2,050.9	1,873.2
Other \| Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	519.7	452.5	1,501.6	1,342.8
Other \| Software
Disaggregation of Revenue [Line Items]
Total Net sales	91.9	102.6	296.1	299.9
Other \| Services
Disaggregation of Revenue [Line Items]
Total Net sales	83.2	81.6	242.1	221.7
Other \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	3.6	3.3	11.1	8.8
United States
Disaggregation of Revenue [Line Items]
Total Net sales	5,023.2	4,863.1	14,793.4	13,892.8
United States \| Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	2,243.0	2,149.4	7,014.7	6,448.0
United States \| Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	427.8	373.0	1,250.3	1,125.9
United States \| Public
Disaggregation of Revenue [Line Items]
Total Net sales	2,346.8	2,333.8	6,511.7	6,298.6
United States \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	5.6	6.9	16.7	20.3
Rest of World
Disaggregation of Revenue [Line Items]
Total Net sales	714.2	653.5	2,119.7	1,919.9
Rest of World \| Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	12.4	11.8	58.2	44.3
Rest of World \| Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	6.0	6.7	19.4	17.6
Rest of World \| Public
Disaggregation of Revenue [Line Items]
Total Net sales	3.0	1.9	7.9	5.1
Rest of World \| Other
Disaggregation of Revenue [Line Items]
Total Net sales	$ 692.8	$ 633.1	$ 2,034.2	$ 1,852.9