NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles

On adoption, using the retrospective method of transition, TEP's Consolidated Statements of Cash Flows included the following adjustments:

	As Filed			Adoption of ASU Impacts		As Adjusted
(in millions)	Year Ended December 31, 2016
Net Cash Flows—Operating Activities	$	425		$	—	$	425
Net Cash Flows—Investing Activities	(376		)	3		(373		)
Net Cash Flows—Financing Activities	(69		)	—		(69		)
Net Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	(20		)	3		(17		)
Cash, Cash Equivalents, and Restricted Cash, Beginning of Period	56			4		60
Cash, Cash Equivalents, and Restricted Cash, End of Period	$	36		$	7	$	43

(in millions)	Year Ended December 31, 2015
Net Cash Flows—Operating Activities	$	365		$	—	$	365
Net Cash Flows—Investing Activities	(503		)	2		(501		)
Net Cash Flows—Financing Activities	120			—		120
Net Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	(18		)	2		(16		)
Cash, Cash Equivalents, and Restricted Cash, Beginning of Period	74			2		76
Cash, Cash Equivalents, and Restricted Cash, End of Period	$	56		$	4	$	60

Restrictions on Cash and Cash Equivalents

The following table presents the line items and amounts of cash, cash equivalents, and restricted cash reported on the balance sheet and reconciles their sum to the cash flow statement:

	Years Ended December 31,
(in millions)	2017		2016		2015
Cash and Cash Equivalents	$	38	$	36	$	56
Restricted Cash included in:
Investments and Other Property	11		7		4
Current Assets, Other	1		—		—
Total Cash, Cash Equivalents, and Restricted Cash	$	50	$	43	$	60

Allowance For Doubtful Accounts

The change in the balance of the Allowance for Doubtful Accounts included in Accounts Receivable, Net on the Consolidated Balance Sheets is summarized as follows:

	Years Ended December 31,
(in millions)	2017			2016			2015
Beginning of Period	$	5		$	27		$	5
Additions Charged to Cost and Expense	3			4			2
Write-offs	(3		)	(3		)	(3		)
Provision for Springerville Unit 1, Third-Party Owners	—			(23		)	23
End of Period	$	5		$	5		$	27

AFUDC Rates

The average AFUDC rates on regulated construction expenditures are included in the table below:

	2017		2016		2015
Average AFUDC Rates	7.31	%	7.47	%	6.12	%

Summary Of Average Annual Depreciation Rates For All Utility Plants

Below are the summarized average annual depreciation rates for all utility plant:

	2017		2016		2015
Average Annual Depreciation Rates	2.97	%	2.85	%	2.83	%