UNS ENERGY EARNINGS PER SHARE - Effects of Dilutive Common Stock on Weighted-Average Number of Shares (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Numerator:
Net Income	$ 67,990		$ 50,664		$ 113,953		$ 83,414
Dilutive Securities, Effect on Basic Earnings Per Share	0	[1]	0	[1]	0	[1]	1,100	[1]
Undistributed Earnings, Diluted	$ 67,990		$ 50,664		$ 113,953		$ 84,514
Weighted Average Shares of Common Stock Outstanding:
Common Shares Issued	41,472		41,290		41,427		39,835
Fully Vested Deferred Stock Units	178		156		169		148
Total Weighted Average Shares of Common Stock Outstanding and Participating Securities - Basic	41,650		41,446		41,596		39,983
Effect of Dilutive Securities:
Incremental Common Shares Attributable to Conversion of Debt Securities	0	[1]	0	[1]	0	[1]	1,417	[1]
Options and Stock Issuable Under Share-Based Compensation Plans	378		417		345		319
Total Shares - Diluted	42,028		41,863		41,941		41,719

[1] In 2012, the Convertible Senior Notes were converted to Common Stock or redeemed for cash.