Business Segments (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Reconciling adjustments of Income Statement items in consolidation
Operating Revenues - External	$ 369,673,000		$ 339,113,000		$ 714,439,000		$ 657,962,000
Income Before Income Taxes	45,873,000		41,842,000		66,721,000		74,233,000
Net Income	28,574,000		25,886,000		41,990,000		46,032,000
Reconciling adjustments of intersegment revenues in consolidation
Wholesale Sales	38,744,000		28,466,000		79,658,000		65,558,000
Gas Revenue - UNS Gas to UNS Electric	25,020,000		24,677,000		82,210,000		80,458,000
Other Revenues	30,293,000		26,030,000		59,740,000		50,230,000
Business Intersegment, Eliminations [Member]
Reconciling adjustments of Income Statement items in consolidation
Operating Revenues - Intersegment	(12,000,000)		(17,000,000)		(23,000,000)		(34,000,000)
Income Before Income Taxes							1,000,000
Net Income							1,000,000
Reconciling adjustments of intersegment revenues in consolidation
Total Intersegment Revenue	(12,000,000)		(17,000,000)		(23,000,000)		(34,000,000)
Business Intersegment, Eliminations [Member] | TEP Segment [Member] | Corporate Services [Member]
Reconciling adjustments of intersegment revenues in consolidation
Other Revenues	2,000,000	[1]	2,000,000	[1]	5,000,000	[1]	4,000,000	[1]
Business Intersegment, Eliminations [Member] | TEP Segment [Member] | Control Area Services [Member]
Reconciling adjustments of intersegment revenues in consolidation
Other Revenues	1,000,000	[2]	1,000,000	[2]	1,000,000	[2]	1,000,000	[2]
Business Intersegment, Eliminations [Member] | Other [Member]
Reconciling adjustments of intersegment revenues in consolidation
Wholesale Sales	3,000,000		3,000,000		5,000,000		5,000,000
Business Intersegment, Eliminations [Member] | Other [Member] | Supplemental Workforce [Member]
Reconciling adjustments of intersegment revenues in consolidation
Other Revenues	4,000,000	[3]	4,000,000	[3]	9,000,000	[3]	8,000,000	[3]
UNS GAS, INC. [Member] | Business Intersegment, Eliminations [Member]
Reconciling adjustments of Income Statement items in consolidation
Operating Revenues - Intersegment			1,000,000
Reconciling adjustments of intersegment revenues in consolidation
Gas Revenue - UNS Gas to UNS Electric	1,000,000				1,000,000		2,000,000
Total Intersegment Revenue			1,000,000
UNS ELECTRIC, INC. [Member] | Business Intersegment, Eliminations [Member]
Reconciling adjustments of intersegment revenues in consolidation
Wholesale Sales					1,000,000		1,000,000
TEP Segment [Member]
Reconciling adjustments of Income Statement items in consolidation
Operating Revenues - External	292,000,000		266,000,000		528,000,000		488,000,000
Operating Revenues - Intersegment	3,000,000		9,000,000		7,000,000		18,000,000
Income Before Income Taxes	40,000,000		43,000,000		47,000,000		59,000,000
Net Income	25,000,000		28,000,000		30,000,000		38,000,000
Reconciling adjustments of intersegment revenues in consolidation
Wholesale Sales			6,000,000	[4]	1,000,000	[4]	13,000,000	[4]
Total Intersegment Revenue	3,000,000		9,000,000		7,000,000		18,000,000
UNS GAS, INC. [Member]
Reconciling adjustments of Income Statement items in consolidation
Operating Revenues - External	25,000,000		25,000,000		84,000,000		81,000,000
Operating Revenues - Intersegment	1,000,000		1,000,000		1,000,000		2,000,000
Income Before Income Taxes	1,000,000		1,000,000		11,000,000		10,000,000
Net Income			1,000,000		7,000,000		6,000,000
Reconciling adjustments of intersegment revenues in consolidation
Total Intersegment Revenue	1,000,000		1,000,000		1,000,000		2,000,000
UNS ELECTRIC, INC. [Member]
Reconciling adjustments of Income Statement items in consolidation
Operating Revenues - External	52,000,000		49,000,000		102,000,000		89,000,000
Operating Revenues - Intersegment	1,000,000				1,000,000		1,000,000
Income Before Income Taxes	5,000,000		3,000,000		8,000,000		8,000,000
Net Income	3,000,000		2,000,000		5,000,000		5,000,000
Reconciling adjustments of intersegment revenues in consolidation
Wholesale Sales	1,000,000
Total Intersegment Revenue	1,000,000				1,000,000		1,000,000
Other [Member]
Reconciling adjustments of Income Statement items in consolidation
Operating Revenues - External	1,000,000		(1,000,000)
Operating Revenues - Intersegment	7,000,000		7,000,000		14,000,000		13,000,000
Income Before Income Taxes			(5,000,000)		1,000,000		(4,000,000)
Net Income	1,000,000		(5,000,000)				(4,000,000)
Reconciling adjustments of intersegment revenues in consolidation
Total Intersegment Revenue	$ 7,000,000		$ 7,000,000		$ 14,000,000		$ 13,000,000

[1] Common costs (systems, facilities, etc.) are allocated on a cost-causative basis and recorded as revenue by TEP. Management believes this method of allocation is reasonable.

[2] TEP charged UNS Electric for control area services based on a FERC approved tariff.

[3] Millennium provides supplemental workforce and meter reading services to TEP, UNS Electric and UNS Gas.

[4] TEP and UNS Electric sell power to each other at prices based on the Dow Jones Four Corners Daily Index.