RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS	9 Months Ended
Sep. 30, 2018
Accounting Changes and Error Corrections [Abstract]
RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS	RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS TEP considers the applicability and impact of all Accounting Standards 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 financial position, results of operations, and 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 with a lease term greater than 12 months and disclosure of additional quantitative and qualitative information about leasing arrangements. The standard is effective for periods beginning January 1, 2019, and is to be applied using a modified retrospective approach or an optional transition method with practical expedient options. The modified retrospective approach requires the restatement of prior periods and presentation of lease disclosures under the new guidance for all periods presented. The optional transition method allows entities to continue to apply the current lease guidance in the comparative periods presented in the year of adoption and apply the transition provisions of the new guidance on the effective date of the new guidance. Early adoption is permitted. In January 2018, the FASB issued an additional optional practical expedient that permits entities to not evaluate existing land easements that were not previously accounted for as leases. TEP plans to adopt this guidance effective January 1, 2019 and will apply the transition provisions of the new standard at the adoption date. The Company expects to elect a package of practical expedients that allows it to not reassess whether any expired or existing contract is a lease or contains a lease, the lease classification of any expired or existing leases, and the initial direct costs for any existing leases. In addition, TEP will elect the practical expedient related to land easements, and the new lease guidance will be applied on a prospective basis to all new or modified land easements. TEP’s leasing activities accounted for as operating leases primarily relate to leases for land and rail cars. The adoption of the new guidance will affect the Company’s Condensed Consolidated Balance Sheets as the Company will be required to record lease assets and lease liabilities related to these operating lease arrangements. TEP is currently identifying and implementing changes to processes and controls and preparing the expanded lease disclosures. The Company does not expect the new ASU to materially affect its balance sheet, results of operations or cash flows. Management continues to monitor standard-setting activities that may affect the transition requirements of the new lease standard. INTERNAL-USE SOFTWARE In August 2018, the FASB issued an ASU that will clarify accounting for implementation costs incurred in a cloud computing arrangement that is a service contract. Under the new guidance, customers will apply the same criteria for capitalizing implementation costs as they would for an arrangement that has a software license. The ASU also provides specific requirements for the classification and presentation of the capitalized implementation costs and the related amortization of those costs. The standard is effective for periods beginning January 1, 2020, and should be applied either retrospectively or prospectively after the date of adoption. Early adoption is permitted. TEP plans to early adopt the new standard prospectively effective January 1, 2019 and does not expect the ASU to have a material impact on its financial statements and disclosures.

RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS

TEP considers the applicability and impact of all Accounting Standards 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 financial position, results of operations, and 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 with a lease term greater than 12 months and disclosure of additional quantitative and qualitative information about leasing arrangements. The standard is effective for periods beginning January 1, 2019, and is to be applied using a modified retrospective approach or an optional transition method with practical expedient options. The modified retrospective approach requires the restatement of prior periods and presentation of lease disclosures under the new guidance for all periods presented. The optional transition method allows entities to continue to apply the current lease guidance in the comparative periods presented in the year of adoption and apply the transition provisions of the new guidance on the effective date of the new guidance. Early adoption is permitted. In January 2018, the FASB issued an additional optional practical expedient that permits entities to not evaluate existing land easements that were not previously accounted for as leases.

TEP plans to adopt this guidance effective January 1, 2019 and will apply the transition provisions of the new standard at the adoption date. The Company expects to elect a package of practical expedients that allows it to not reassess whether any expired or existing contract is a lease or contains a lease, the lease classification of any expired or existing leases, and the initial direct costs for any existing leases. In addition, TEP will elect the practical expedient related to land easements, and the new lease guidance will be applied on a prospective basis to all new or modified land easements.

TEP’s leasing activities accounted for as operating leases primarily relate to leases for land and rail cars. The adoption of the new guidance will affect the Company’s Condensed Consolidated Balance Sheets as the Company will be required to record lease assets and lease liabilities related to these operating lease arrangements. TEP is currently identifying and implementing changes to processes and controls and preparing the expanded lease disclosures. The Company does not expect the new ASU to materially affect its balance sheet, results of operations or cash flows. Management continues to monitor standard-setting activities that may affect the transition requirements of the new lease standard.

INTERNAL-USE SOFTWARE

In August 2018, the FASB issued an ASU that will clarify accounting for implementation costs incurred in a cloud computing arrangement that is a service contract. Under the new guidance, customers will apply the same criteria for capitalizing implementation costs as they would for an arrangement that has a software license. The ASU also provides specific requirements for the classification and presentation of the capitalized implementation costs and the related amortization of those costs. The standard is effective for periods beginning January 1, 2020, and should be applied either retrospectively or prospectively after the date of adoption. Early adoption is permitted. TEP plans to early adopt the new standard prospectively effective January 1, 2019 and does not expect the ASU to have a material impact on its financial statements and disclosures.