RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS	12 Months Ended
Dec. 31, 2017
Disclosure Text Block [Abstract]
RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS	RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS TEP considers the applicability and impact of all Accounting Standard Updates (ASU) issued by the Financial Accounting Standards Board (FASB). The following updates have been issued, but have not yet been adopted by TEP. Updates not listed below were assessed and either determined to not be applicable or are expected to have a minimal impact on TEP's consolidated financial position, results of operations, or disclosures. REVENUE FROM CONTRACTS WITH CUSTOMERS In May 2014, the FASB issued an ASU intended to enable users of financial statements to better understand and consistently analyze an entity's revenues across industries and transactions. The ASU was effective for annual and interim periods beginning January 1, 2018 and permits two implementation approaches: (i) retrospective application; or (ii) modified retrospective application by recognizing the cumulative effect of initially applying the guidance as an adjustment to the opening balance of retained earnings on the date of adoption supplemented by additional disclosures. TEP adopted this ASU on January 1, 2018, using the modified retrospective approach, and did not identify or record any adjustment to the opening balance of retained earnings on adoption. Under the new standard, recognition of revenue occurs when a customer obtains control of promised goods or services. In addition, the ASU requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The adoption of this ASU did not affect revenue recognition for tariff-based sales to retail and wholesale customers, which represent TEP's primary source of revenue. Accordingly, the adoption of this standard did not have a material effect on TEP's financial statements. However, the presentation and disclosure requirements of the ASU will result in a change in the presentation of revenues on TEP's income statement as well as expanded disclosures. LEASES In February 2016, the FASB issued an ASU that will require the recognition of leased assets and liabilities by lessees for those leases classified as operating leases under current GAAP. The standard is effective for periods beginning January 1, 2019, and is to be applied using a modified retrospective approach with practical expedient options. Early adoption is permitted. TEP is evaluating the impact of this ASU to its financial statements and disclosures. COMPENSATION—RETIREMENT BENEFITS In March 2017, the FASB issued an ASU to improve the presentation of net periodic benefit cost for pension and other postretirement benefits. TEP adopted this ASU on January 1, 2018, the effective date of the ASU. Effective in the first quarter of 2018, TEP will no longer capitalize the non-service cost components of net periodic benefit cost as part of inventory or plant in service and will present non-service costs retrospectively in Other Income—Other Expense on the Consolidated Statements of Income. The adoption of the ASU did not have a material impact on the Company's financial position or results of operations. DERIVATIVES AND HEDGING In August 2017, the FASB issued an ASU that enables entities to better align their risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance and the presentation of hedge results. The ASU expands an entity's ability to apply hedge accounting to non-financial and financial risk components and simplify fair value hedges of interest rate risk. The ASU eliminates the requirement to separately measure and report hedge ineffectiveness and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The amendments to the ASU also ease hedge documentation and effectiveness assessments requirements under previous guidance. The standard is effective for fiscal years beginning January 1, 2019. Early adoption is permitted. The ASU is expected to have minimal impact to TEP's financial statements and disclosures.

RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS

TEP considers the applicability and impact of all Accounting Standard Updates (ASU) issued by the Financial Accounting Standards Board (FASB). The following updates have been issued, but have not yet been adopted by TEP. Updates not listed below were assessed and either determined to not be applicable or are expected to have a minimal impact on TEP's consolidated financial position, results of operations, or disclosures.

REVENUE FROM CONTRACTS WITH CUSTOMERS

In May 2014, the FASB issued an ASU intended to enable users of financial statements to better understand and consistently analyze an entity's revenues across industries and transactions. The ASU was effective for annual and interim periods beginning January 1, 2018 and permits two implementation approaches: (i) retrospective application; or (ii) modified retrospective application by recognizing the cumulative effect of initially applying the guidance as an adjustment to the opening balance of retained earnings on the date of adoption supplemented by additional disclosures. TEP adopted this ASU on January 1, 2018, using the modified retrospective approach, and did not identify or record any adjustment to the opening balance of retained earnings on adoption. Under the new standard, recognition of revenue occurs when a customer obtains control of promised goods or services. In addition, the ASU requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The adoption of this ASU did not affect revenue recognition for tariff-based sales to retail and wholesale customers, which represent TEP's primary source of revenue. Accordingly, the adoption of this standard did not have a material effect on TEP's financial statements. However, the presentation and disclosure requirements of the ASU will result in a change in the presentation of revenues on TEP's income statement as well as expanded disclosures.

LEASES

In February 2016, the FASB issued an ASU that will require the recognition of leased assets and liabilities by lessees for those leases classified as operating leases under current GAAP. The standard is effective for periods beginning January 1, 2019, and is to be applied using a modified retrospective approach with practical expedient options. Early adoption is permitted. TEP is evaluating the impact of this ASU to its financial statements and disclosures.

COMPENSATION—RETIREMENT BENEFITS

In March 2017, the FASB issued an ASU to improve the presentation of net periodic benefit cost for pension and other postretirement benefits. TEP adopted this ASU on January 1, 2018, the effective date of the ASU. Effective in the first quarter of 2018, TEP will no longer capitalize the non-service cost components of net periodic benefit cost as part of inventory or plant in service and will present non-service costs retrospectively in Other Income—Other Expense on the Consolidated Statements of Income. The adoption of the ASU did not have a material impact on the Company's financial position or results of operations.

DERIVATIVES AND HEDGING

In August 2017, the FASB issued an ASU that enables entities to better align their risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance and the presentation of hedge results. The ASU expands an entity's ability to apply hedge accounting to non-financial and financial risk components and simplify fair value hedges of interest rate risk. The ASU eliminates the requirement to separately measure and report hedge ineffectiveness and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The amendments to the ASU also ease hedge documentation and effectiveness assessments requirements under previous guidance. The standard is effective for fiscal years beginning January 1, 2019. Early adoption is permitted. The ASU is expected to have minimal impact to TEP's financial statements and disclosures.