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								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Numerator:
Net Income	$ 13,525	$ 67,990	$ 34,618	$ 11,345	$ 7,506	$ 50,664	$ 26,273	$ 6,476	$ 127,478		$ 90,919		$ 109,975
Interest on Convertible Debt, Net of Tax									0	[1]	1,100	[1]	4,390	[1]
Adjusted Net Income Available for Diluted Common Stock Outstanding									$ 127,478		$ 92,019		$ 114,365
Weighted Average Shares of Common Stock Outstanding:
Common Shares Issued									41,446		40,212		36,780
Fully Vested Deferred Stock Units									172		150		129
Participating Securities									0		0		53
Total Weighted Average Shares of Common Stock Outstanding and Participating Securities - Basic									41,618		40,362		36,962
Effect of Dilutive Securities:
Convertible Senior Notes									0	[1]	1,062	[1]	4,281	[1]
Options and Stock Issuable Under Share-Based Compensation Plans									357		331		366
Total Shares - Diluted									41,975		41,755		41,609

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