FAIR VALUE MEASUREMENTS & DERIVATIVE INSTRUMENTS (Quantitative Information Regarding Unobservable Inputs) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 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	6
Level 3 [Member] | Market Approach Valuation Technique [Member] | Forward Contracts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	3	[2]
Derivative Liability	5	[2]
Level 3 [Member] | Valuation Technique Option Model [Member] | Options Held [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	3	[3]
Derivative Liability	1	[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	25.05
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	3.77
Gas volatility	19.81%
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	60.10
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	4.66
Gas volatility	31.62%
TUCSON ELECTRIC POWER COMPANY
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	4	[1]	2	[1]
TUCSON ELECTRIC POWER COMPANY | Level 3 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Derivative Assets	2	[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	1
Derivative Liability	(4)	[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] 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 UNS Energy and TEP balance sheets. The valuation techniques are described below.

[2] TEP comprises $1 million of the forward contract assets and $4 million of the forward contract liabilities.

[3] TEP comprises $1 million of the option contract assets.