DEBT, CREDIT FACILITIES, AND CAPITAL LEASE OBLIGATIONS (Credit agreements) (Details) (USD $)		12 Months Ended			12 Months Ended								12 Months Ended
	Dec. 31, 2010 TUCSON ELECTRIC POWER COMPANY Letter of Credit [Member]	Dec. 31, 2013 UNS Gas and UNS Electric [Member] Line of Credit [Member]	Dec. 31, 2013 Parent [Member] Line of Credit [Member]	Feb. 25, 2014 Subsequent Event [Member] TUCSON ELECTRIC POWER COMPANY Letter of Credit [Member]	Dec. 31, 2013 Revolving Credit Facility [Member] TUCSON ELECTRIC POWER COMPANY Line of Credit [Member]	Dec. 31, 2013 Revolving Credit Facility [Member] UNS Gas and UNS Electric [Member] Line of Credit [Member]	Dec. 31, 2013 Revolving Credit Facility [Member] Parent [Member] Line of Credit [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Parent [Member] Line of Credit [Member]	Dec. 31, 2013 Revolving Credit Facility [Member] UNS ELECTRIC, INC. Line of Credit [Member]	Feb. 14, 2014 Revolving Credit Facility [Member] Subsequent Event [Member] TUCSON ELECTRIC POWER COMPANY Line of Credit [Member]	Feb. 25, 2014 Revolving Credit Facility [Member] Subsequent Event [Member] Parent [Member] Line of Credit [Member]	Feb. 14, 2014 Revolving Credit Facility [Member] Subsequent Event [Member] UNS ELECTRIC, INC. Line of Credit [Member]	Dec. 31, 2013 Letter of Credit [Member] TUCSON ELECTRIC POWER COMPANY Line of Credit [Member]	Nov. 30, 2013 Letter of Credit [Member] TUCSON ELECTRIC POWER COMPANY Line of Credit [Member]	Dec. 31, 2012 Letter of Credit [Member] TUCSON ELECTRIC POWER COMPANY Line of Credit [Member]	Dec. 31, 2013 Letter of Credit [Member] UNS ELECTRIC, INC. Line of Credit [Member]	Dec. 31, 2012 Letter of Credit [Member] UNS ELECTRIC, INC. Line of Credit [Member]	Feb. 14, 2014 Letter of Credit [Member] Subsequent Event [Member] TUCSON ELECTRIC POWER COMPANY Line of Credit [Member]	Feb. 14, 2014 Letter of Credit [Member] Subsequent Event [Member] UNS ELECTRIC, INC. Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility borrowing capacity		$ 100,000,000	$ 125,000,000		$ 200,000,000									$ 186,000,000
Letters of credit outstanding													82,000,000
Outstanding borrowings under the company credit agreement	37,000,000				0		54,000,000	45,000,000	22,000,000	90,000,000	52,000,000	25,000,000	1,000,000		1,000,000	500,000	500,000	1,000,000	500,000
Average interest rate							1.70%	2.00%
Interest rate spread on LIBOR borrowing					1.125%	1.125%	1.25%						1.125%
Interest rate in addition to alternate base rate for alternate base rate loans					0.125%	0.125%	0.25%
Maximum borrowings outstanding limit		70,000,000
Letter of credit cancelled													$ 104,000,000
Commitment fee percentage				1.00%