FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Level 3 Fair Value Measurements) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	$ 11	[1]	$ 7	[1]
Level 3 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	6	[1]	4	[1]
Derivative Liability	(5)		(6)
Level 3 [Member] | Market Approach Valuation Technique [Member] | Forward Contracts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	4	[2]	1	[2]
Derivative Liability	(4)	[2]	(4)	[2]
Level 3 [Member] | Valuation Technique Option Model [Member] | Options Held [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	2	[3]	3	[3]
Derivative Liability	(1)	[3]	(2)	[3]
Minimum [Member] | Level 3 [Member] | Market Approach Valuation Technique [Member] | Forward Contracts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Market price per MWh	23.90		26.54
Minimum [Member] | Level 3 [Member] | Valuation Technique Option Model [Member] | Options Held [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Market price per MMbtu	3.87		3.87
Gas volatility	21.01%		25.05%
Maximum [Member] | Level 3 [Member] | Market Approach Valuation Technique [Member] | Forward Contracts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Market price per MWh	57.90		51.75
Maximum [Member] | Level 3 [Member] | Valuation Technique Option Model [Member] | Options Held [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Market price per MMbtu	4.57		4.32
Gas volatility	32.10%		35.07%
TUCSON ELECTRIC POWER COMPANY
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	5	[1]	2	[1]
TUCSON ELECTRIC POWER COMPANY | Level 3 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	3	[1]	1	[1]
TUCSON ELECTRIC POWER COMPANY | Level 3 [Member] | Market Approach Valuation Technique [Member] | Forward Contracts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	2	[2]
Derivative Liability	(2)	[2]
TUCSON ELECTRIC POWER COMPANY | Level 3 [Member] | Valuation Technique Option Model [Member] | Forward Contracts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets			1	[2]
Derivative Liability			(3)	[2]
TUCSON ELECTRIC POWER COMPANY | Level 3 [Member] | Valuation Technique Option Model [Member] | Options Held [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	1		1
Derivative Liability	$ (1)

[1] Energy Contracts include gas swap agreements (Level 2), power options (Level 2), gas options (Level 3), and forward power purchase and sales contracts (Level 3) entered into to reduce exposure to energy price risk. These contracts are included in Derivative Instruments on the balance sheets. The valuation techniques are described below.

[2] TEP comprises $2 million of the forward contract assets and $2 million of the forward contract liabilities at June 30, 2014.

[3] TEP comprises $1 million of the option contract assets and $1 million of the option contract liabilities at June 30, 2014.