Nature of Operations and Basis of Accounting Presentation (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended		72 Months Ended	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended					6 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended					6 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended					6 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended			6 Months Ended		12 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Mar. 31, 2011 TEP [Member] Scenario, Adjustment [Member]	Dec. 31, 2010 TEP [Member] Scenario, Adjustment [Member]	Jun. 30, 2010 TEP [Member] Scenario, Adjustment [Member]	Mar. 31, 2010 TEP [Member] Scenario, Adjustment [Member]	Jun. 30, 2010 TEP [Member] Scenario, Adjustment [Member]	Sep. 30, 2010 TEP [Member] Scenario, Adjustment [Member]	Dec. 31, 2010 TEP [Member] Scenario, Adjustment [Member]	Dec. 31, 2009 TEP [Member] Scenario, Adjustment [Member]	Mar. 31, 2011 Scenario, Adjustment [Member]	Dec. 31, 2010 Scenario, Adjustment [Member]	Sep. 30, 2010 Scenario, Adjustment [Member]	Jun. 30, 2010 Scenario, Adjustment [Member]	Mar. 31, 2010 Scenario, Adjustment [Member]	Jun. 30, 2010 Scenario, Adjustment [Member]	Sep. 30, 2010 Scenario, Adjustment [Member]	Dec. 31, 2010 Scenario, Adjustment [Member]	Dec. 31, 2009 Scenario, Adjustment [Member]	Mar. 31, 2011 TEP [Member] Scenario, Previously Reported [Member]	Dec. 31, 2010 TEP [Member] Scenario, Previously Reported [Member]	Sep. 30, 2010 TEP [Member] Scenario, Previously Reported [Member]	Jun. 30, 2010 TEP [Member] Scenario, Previously Reported [Member]	Mar. 31, 2010 TEP [Member] Scenario, Previously Reported [Member]	Jun. 30, 2010 TEP [Member] Scenario, Previously Reported [Member]	Sep. 30, 2010 TEP [Member] Scenario, Previously Reported [Member]	Dec. 31, 2010 TEP [Member] Scenario, Previously Reported [Member]	Dec. 31, 2009 TEP [Member] Scenario, Previously Reported [Member]	Mar. 31, 2011 Scenario, Previously Reported [Member]	Dec. 31, 2010 Scenario, Previously Reported [Member]	Sep. 30, 2010 Scenario, Previously Reported [Member]	Jun. 30, 2010 Scenario, Previously Reported [Member]	Mar. 31, 2010 Scenario, Previously Reported [Member]	Jun. 30, 2010 Scenario, Previously Reported [Member]	Sep. 30, 2010 Scenario, Previously Reported [Member]	Dec. 31, 2010 Scenario, Previously Reported [Member]	Dec. 31, 2009 Scenario, Previously Reported [Member]	Jun. 30, 2011 TEP [Member]	Sep. 30, 2010 TEP [Member]	Jun. 30, 2010 TEP [Member]	Jun. 30, 2011 TEP [Member]	Jun. 30, 2010 TEP [Member]	Dec. 31, 2010 TEP [Member]	Dec. 31, 2009 TEP [Member]	Jun. 30, 2010 Millennium Energy Holdings [Member]	Jun. 30, 2011 Millennium Energy Holdings [Member]	Jun. 30, 2010 UNS GAS, INC. [Member]	Jun. 30, 2011 UNS GAS, INC. [Member]	Jun. 30, 2010 UNS GAS, INC. [Member]	Jun. 30, 2011 UNS ELECTRIC, INC. [Member]	Jun. 30, 2010 UNS ELECTRIC, INC. [Member]	Jun. 30, 2011 UNS ELECTRIC, INC. [Member]	Jun. 30, 2010 UNS ELECTRIC, INC. [Member]
Income Statement
Electric Wholesale Sales	$ 38,744,000	$ 28,466,000	$ 79,658,000	$ 65,558,000				$ 35,255,000	$ 44,107,000	$ 29,276,000	$ 40,990,000	$ 70,265,000	$ 96,996,000	$ 141,103,000	$ 153,306,000	$ 40,913,000	$ 49,565,000	$ 36,838,000	$ 28,466,000	$ 37,093,000	$ 65,558,000	$ 102,397,000	$ 151,962,000	$ 131,255,000	$ 35,122,000	$ 46,121,000	$ 26,669,000	$ 27,983,000	$ 40,962,000	$ 68,025,000	$ 94,694,000	$ 140,815,000	$ 152,955,000	$ 40,781,000	$ 51,579,000	$ 36,776,000	$ 27,174,000	$ 37,064,000	$ 63,319,000	$ 100,094,000	$ 151,673,000	$ 130,904,000	$ 31,759,000	$ 26,731,000	$ 29,276,000	$ 67,015,000	$ 70,265,000								$ 1,000,000
Fuel	82,563,000	69,304,000	154,692,000	129,909,000				71,308,000	75,444,000	66,753,000	58,507,000	125,260,000	211,228,000	286,672,000	281,481,000	72,130,000	77,003,000	90,668,000	69,304,000	60,605,000	129,909,000	220,577,000	297,580,000	298,426,000	71,315,000	75,233,000	85,793,000	66,694,000	58,351,000	125,045,000	210,838,000	286,071,000	281,710,000	72,137,000	76,793,000	90,493,000	69,246,000	60,448,000	129,694,000	220,187,000	296,980,000	298,655,000	80,831,000	85,968,000	66,753,000	152,138,000	125,260,000
Purchased Power	66,336,000	66,591,000	144,610,000	149,396,000				17,236,000	12,815,000	33,337,000	24,654,000	57,992,000	105,901,000	118,716,000	144,529,000	78,274,000	64,003,000	93,889,000	66,591,000	82,805,000	149,396,000	243,285,000	307,288,000	296,861,000	16,601,000	14,950,000	47,909,000	32,122,000	24,654,000	55,857,000	103,766,000	118,716,000	144,528,000	77,640,000	66,137,000	93,889,000	65,376,000	82,805,000	147,261,000	241,151,000	307,288,000	296,861,000		47,909,000
Increase (Decrease) to Reflect PPFAC/PGA Recovery Treatment	3,227,000	(10,313,000)	(3,008,000)	(23,058,000)				9,783,000	(992,000)	7,601,000	3,232,000	10,833,000	24,299,000	23,307,000	20,190,000	6,235,000	(4,148,000)	12,478,000	10,313,000	12,745,000	23,058,000	35,536,000	31,388,000	16,558,000	9,342,000	(1,073,000)	13,362,000	7,618,000	3,118,000	10,736,000	24,098,000	23,025,000	20,724,000	5,793,000	(4,320,000)	12,373,000	10,330,000	12,631,000	22,962,000	35,335,000	31,105,000	17,091,000		13,467,000
Income Tax Expense	17,299,000	15,956,000	24,731,000	28,201,000				2,491,000	1,456,000	14,728,000	6,224,000	20,952,000	58,404,000	59,860,000	54,028,000	7,432,000	4,870,000	43,773,000	15,956,000	12,247,000	28,202,000	71,975,000	76,845,000	63,040,000	208,000	1,543,000	38,139,000	15,028,000	6,348,000	21,376,000	59,514,000	61,057,000	55,130,000	3,909,000	5,000,000	44,533,000	16,300,000	12,435,000	28,735,000	73,266,000	78,266,000	64,348,000	15,133,000	37,452,000	14,728,000	17,624,000	20,953,000
Net Income	28,574,000	25,886,000	41,990,000	46,032,000				4,648,000	10,075,000	27,938,000	10,458,000	38,396,000	98,069,000	108,144,000	90,396,000	13,416,000	11,202,000	55,635,000	25,886,000	20,146,000	46,032,000	101,667,000	112,868,000	105,608,000	6,983,000	9,999,000	58,993,000	27,636,000	10,349,000	37,986,000	96,979,000	106,978,000	89,248,000	16,992,000	11,082,000	54,883,000	25,540,000	19,972,000	45,513,000	100,395,000	111,477,000	104,258,000	25,128,000	59,673,000	27,938,000	29,776,000	38,396,000					1,000,000	7,000,000	6,000,000	3,000,000	2,000,000	5,000,000	5,000,000
Basic Earnings Per Share (EPS)	$ 0.77	$ 0.71	$ 1.14	$ 1.27												$ 0.36	$ 0.31	$ 1.52	$ 0.71	$ 0.56	$ 1.27	$ 2.8	$ 3.1	$ 2.95										$ 0.46	$ 0.3	$ 1.5	$ 0.7	$ 0.55	$ 1.26	$ 2.76	$ 3.06	$ 2.91
Diluted EPS	$ 0.71	$ 0.66	$ 1.07	$ 1.18												$ 0.35	$ 0.3	$ 1.38	$ 0.66	$ 0.52	$ 1.18	$ 2.56	$ 2.86	$ 2.72										$ 0.44	$ 0.29	$ 1.36	$ 0.65	$ 0.52	$ 1.17	$ 2.53	$ 2.82	$ 2.69
Balance Sheets
Deferred Income Taxes - Current	34,839,000		34,839,000		32,386,000			33,584,000	33,640,000	47,670,000	47,232,000	47,670,000		33,640,000	48,135,000	32,588,000	32,386,000	52,059,000	47,417,000	48,457,000	47,417,000	52,059,000	32,386,000	49,701,000	36,205,000	36,283,000	55,323,000	50,319,000	49,881,000	50,319,000	55,323,000	36,283,000	50,789,000	35,210,000	35,028,000	54,705,000	50,066,000	51,106,000	50,066,000	54,705,000	35,028,000	52,355,000	35,723,000	52,677,000		35,723,000		33,640,000
Accounts Receivable - Customer	94,618,000		94,618,000		91,556,000			60,553,000	71,424,000	71,342,000	60,669,000	71,342,000		71,424,000	70,456,000	80,343,000	91,556,000	117,636,000	86,342,000	75,060,000	86,342,000	117,636,000	91,556,000	88,138,000	53,560,000	63,916,000	92,197,000	63,627,000	54,957,000	63,627,000	92,197,000	63,916,000	62,508,000	73,350,000	84,048,000	110,014,000	78,626,000	69,543,000	78,626,000	110,014,000	84,048,000	80,191,000	76,988,000	99,819,000		76,988,000		71,425,000
Regulatory Assets - Noncurrent	166,311,000		166,311,000		196,736,000			180,913,000	186,074,000	142,209,000	137,641,000	142,209,000		186,074,000	138,466,000	191,429,000	196,737,000	189,421,000	154,576,000	149,236,000	154,576,000	189,421,000	196,737,000	150,324,000	180,723,000	182,514,000	170,287,000	140,102,000	136,013,000	140,102,000	170,287,000	182,514,000	137,147,000	191,238,000	191,124,000	184,097,000	150,608,000	145,821,000	150,608,000	184,097,000	191,124,000	147,325,000	156,345,000	173,631,000		156,345,000		186,074,000
Common Stock Equity	847,095,000		847,095,000		828,368,000			712,609,000	707,495,000	698,313,000	672,247,000	698,313,000		707,495,000	648,319,000	828,133,000	828,368,000	823,996,000	779,544,000	764,303,000	779,544,000	823,996,000	828,368,000	757,056,000	708,604,000	701,155,000	720,063,000	692,729,000	666,963,000	692,729,000	720,063,000	701,155,000	643,144,000	824,127,000	820,786,000	816,533,000	772,833,000	757,939,000	772,833,000	816,533,000	820,786,000	750,865,000	736,916,000	726,328,000		736,916,000		707,495,000
Accounts Payable - Trade	123,508,000		123,508,000		109,896,000			71,833,000	77,966,000	92,189,000	78,539,000	92,189,000		77,966,000	72,032,000	97,817,000	109,896,000	102,964,000	108,383,000	100,634,000	108,383,000	102,964,000	109,896,000	99,694,000	71,276,000	77,389,000	81,291,000	91,606,000	77,840,000	91,606,000	81,291,000	77,389,000	71,328,000	97,260,000	109,318,000	102,363,000	107,800,000	99,936,000	107,800,000	102,363,000	109,318,000	98,990,000	98,251,000	81,891,000		98,251,000		77,967,000
Deferred Income Taxes - Noncurrent	268,265,000		268,265,000		246,466,000			224,564,000	227,615,000	231,247,000	221,908,000	231,247,000		227,615,000	218,049,000	248,060,000	246,466,000	293,008,000	246,183,000	235,197,000	246,183,000	293,008,000	246,466,000	228,596,000	224,564,000	226,107,000	268,385,000	230,241,000	221,098,000	230,241,000	268,385,000	226,107,000	217,316,000	248,060,000	244,148,000	290,772,000	244,441,000	233,681,000	244,441,000	290,772,000	244,148,000	227,199,000	241,409,000	269,839,000		241,409,000		227,615,000
Nature of Operations and Basis of Accounting Presentation (Textuals) [Abstract]
Percentage of Unisource Energy's assets represented by Tucson Electric Power Company (TEP)																																											81.00%			81.00%
Customers																																											403,000			403,000							146,000		91,000		91,000
Operating location																																											1,155 square mile area in Southern Arizona			1,155 square mile area in Southern Arizona
Millennium's investments in unregulated businesses as percentage of UniSource Energy's assets																																																			less than 1 %
Impairment losses, net																																																		13,000,000
Increase in Net income due to revised prior period financial statements					1,000,000	1,000,000																																										1,000,000	1,000,000
Increase in net income due to after tax adjustment related to periods prior to 2009							$ 5,000,000																																							$ 5,000,000