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Textuals (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) numberOfPlans | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined contribution plan, employer discretionary contribution amount |  |  |  | $ 20,600 |
Defined contribution plan, cost recognized | $ 18,300 | $ 22,900 |  | 42,900 |
Assets Held-in-trust | $ 39,600 |  |  |  |
Defined Benefit Plan, Description | WESCO sponsors a contributory defined benefit plan (the "EECOL Plan") covering substantially all Canadian employees of EECOL. The EECOL Plan provides retirement benefits based on earnings and credited service, and participants contribute 2% of their earnings to the EECOL Plan. Participants become 100% vested after two years of continuous service or, if earlier, at the participant's normal retirement age. |  |  |  |
Defined Benefit Plan, Unfunded Plan | WESCO also sponsors a Supplemental Executive Retirement Plan (the "EECOL SERP"), which provides additional pension benefits to certain executives of EECOL based on earnings, and credited service. Effective January 1, 2013, the EECOL SERP was closed to new participants and existing participants became 100% vested. EECOL SERP participants continue to contribute 4% of their earnings to the EECOL Plan. |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 2.20% | 3.20% | [1] |  |
Defined Benefit Plan, Benefit Obligation | $ 819,339 | $ 134,852 | [1] | 105,515 | [1]
DefinedBenefitPlanNumberOfPlansWithProjectedBenefitObligationsInExcessOfFairValueOfPlanAssets | numberOfPlans | 13 |  |  |  |
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation | $ 504,800 |  |  |  |
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets | 365,400 |  |  |  |
Defined Benefit Plan, Plan Assets, Amount | $ 721,005 | 103,385 | [1] | 86,556 | [1]
Accumulated Benefit Obligation (ABO) at December 31 |  | 104,600 |  |  |
DefinedBenefitPlanNumberOfPlansWithAccumulatedBenefitObligationsInExcessOfFairValueOfPlanAssets | numberOfPlans | 13 |  |  |  |
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation | $ 435,600 |  |  |  |
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets | 365,400 |  |  |  |
Service Cost | $ 10,792 | 4,602 | [1] | 5,242 |
Defined Benefit Plan Assets Actual Gain Loss | 13.60% |  |  |  |
Defined Benefit Plan, Expected Future Benefit Payment, Year One | $ 38,400 |  |  |  |
WESCO [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined contribution plan, employer matching contribution, percent | 50.00% |  |  |  |
Defined contribution plan, maximum annual contribution per employee, percent | 6.00% |  |  |  |
Anixter Employee Savings Plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined contribution plan, employer matching contribution, percent | 50.00% |  |  |  |
Defined contribution plan, maximum annual contribution per employee, percent | 5.00% |  |  |  |
WESCO Deferred Compensation Plan |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Deferred Compensation Liability, Current | $ 10,100 |  |  |  |
Deferred Compensation Liability, Classified, Noncurrent | 17,300 | $ 25,200 |  |  |
AnixterDeferred Compensation Plan |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Deferred Compensation Liability, Current | $ 45,100 |  |  |  |
Foreign Plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 2.00% | 3.20% | [1] |  |
Defined Benefit Plan, Benefit Obligation | $ 486,855 | $ 134,852 | [1] | 105,515 | [1]
Defined Benefit Plan, Plan Assets, Amount | 365,718 | 103,385 | [1] | 86,556 | [1]
Accumulated Benefit Obligation (ABO) at December 31 | 417,600 |  |  |  |
Service Cost | 9,029 | $ 4,602 | [1] | 5,242 |
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year | 11,400 |  |  |  |
Defined Benefit Plan, Expected Future Benefit Payment, Year One | $ 9,873 |  |  |  |
United States |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 2.60% | 0.00% |  |  |
Defined Benefit Plan, Benefit Obligation | $ 332,484 | $ 0 |  | 0 |
Defined Benefit Plan, Plan Assets, Amount | 355,287 | 0 |  | 0 |
Accumulated Benefit Obligation (ABO) at December 31 | 328,200 |  |  |  |
Service Cost | 1,763 | 0 |  | 0 |
Defined Benefit Plan, Expected Future Benefit Payment, Year One | $ 28,527 |  |  |  |
Minimum | WESCO Distribution Canada Defined Contribution plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined contribution plan, employer matching contribution, percent | 3.00% |  |  |  |
Minimum | Anixter Employee Savings Plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined contribution discretionary contribution percentage | 2.00% |  |  |  |
Maximum | WESCO Distribution Canada Defined Contribution plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined contribution plan, employer matching contribution, percent | 5.00% |  |  |  |
Maximum | Anixter Employee Savings Plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined contribution discretionary contribution percentage | 2.50% |  |  |  |
Pension Plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Other Nonoperating Gains (Losses) | $ (8,200) | $ (1,400) |  | $ (1,900) |
Pension Plan [Member] | Foreign Plan [Member] |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined Benefit Plan, Benefit Obligation | 486,800 |  |  |  |
Pension Plan [Member] | United States |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Defined Benefit Plan, Expected Future Benefit Payment, Year One | 18,100 |  |  |  |
WESCO Deferred Compensation Plan |  |  |  |  |
Schedule of Employee Benefit Plans [Line Items] |  |  |  |  |
Deferred Compensation Liability, Current and Noncurrent | $ 27,400 |  |  |  |
[1] | For 2019, the changes in benefit obligations, plan assets and funded status relate to the EECOL Plan and the EECOL SERP

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- Details
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