INCOME TAXES	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	11. INCOME TAXES The effective tax rate for the three months ended March 31, 2018 and 2017 was 19.6% and 25.0%, respectively. WESCO’s effective tax rate is typically impacted by the tax effect of intercompany financing, foreign tax rate differences, other nondeductible expenses and state income taxes. The lower effective tax rate for the three months ended March 31, 2018 was primarily due to the Tax Cuts and Jobs Act of 2017 (the "TCJA"), which permanently reduced the U.S. federal statutory income tax rate from 35% to 21%, effective January 1, 2018. There were no material discrete items for the three months ended March 31, 2018. In the first quarter of 2017, the application of ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, resulted in a discrete benefit from the exercise and vesting of stock-based awards, which lowered the effective tax rate by 3.1 percentage points. As of March 31, 2018, provisional amounts are recorded for certain income tax effects of the TCJA for which the accounting is incomplete, but a reasonable estimate can be determined. Future adjustments (if any) will be recognized as discrete income tax expense or benefit in the period the adjustments are determined.

11. INCOME TAXES

The effective tax rate for the three months ended March 31, 2018 and 2017 was 19.6% and 25.0%, respectively. WESCO’s effective tax rate is typically impacted by the tax effect of intercompany financing, foreign tax rate differences, other nondeductible expenses and state income taxes. The lower effective tax rate for the three months ended March 31, 2018 was primarily due to the Tax Cuts and Jobs Act of 2017 (the "TCJA"), which permanently reduced the U.S. federal statutory income tax rate from 35% to 21%, effective January 1, 2018. There were no material discrete items for the three months ended March 31, 2018. In the first quarter of 2017, the application of ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, resulted in a discrete benefit from the exercise and vesting of stock-based awards, which lowered the effective tax rate by 3.1 percentage points.

As of March 31, 2018, provisional amounts are recorded for certain income tax effects of the TCJA for which the accounting is incomplete, but a reasonable estimate can be determined. Future adjustments (if any) will be recognized as discrete income tax expense or benefit in the period the adjustments are determined.