approximate percent of net periodic benefit cost capitalized to construction

No definition available.

Name:	uns_Capitalizednetperiodicbenefitcost
Namespace Prefix:	uns_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined Benefit Plan, Expected Future Benefit Payments, Next Five Years

+ References

No definition available.

+ Details

Name:	uns_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextFiveYears
Namespace Prefix:	uns_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Defined Benefit Plan, Expected Future Benefit Payments, Year Six to Ten

+ References

No definition available.

+ Details

Name:	uns_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearSixtoTen
Namespace Prefix:	uns_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Change in future payments due to plan amendment

+ References

No definition available.

+ Details

Name:	uns_EffectofPlanAmendmentonFuturePayments
Namespace Prefix:	uns_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Index value as percentage of real estate.

+ References

No definition available.

+ Details

Name:	uns_IndexValueAsPercentageOfRealEstate
Namespace Prefix:	uns_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	uns_PensionPlansPostretirementAndOtherEmployeeBenefitsLineItems
Namespace Prefix:	uns_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Accumulated Benefit Obligation

-URI http://asc.fasb.org/extlink&oid=6503844

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Glossary Plan Amendment

-URI http://asc.fasb.org/extlink&oid=6520743

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Plan Amendment

-URI http://asc.fasb.org/extlink&oid=6520782

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)(7)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAmendments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

EMPLOYEE BENEFIT PLANS (Additional Information) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentage of net periodic benefit cost that was capitalized	21.00%
Level 3 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Index value percentage of real estate assets	85.00%	87.00%
Other Retiree Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	$ 6	$ 5
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	23	23
Defined Benefit Plan, Accumulated Benefit Obligation	314	334
TUCSON ELECTRIC POWER COMPANY
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Matching 401(k) contributions made	5	5	5
TUCSON ELECTRIC POWER COMPANY \| Other Retiree Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	6	5
TUCSON ELECTRIC POWER COMPANY \| Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	22	20
UNS Gas and UNS Electric [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Expected annual benefit payment for 2014-2018	7
Expected annual benefit payment for 2019-2023	9
Matching 401(k) contributions made	1	1	1
Other Retiree Benefits [Member] \| TUCSON ELECTRIC POWER COMPANY
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Effect of plan amendment on obligation		1
Pension Benefits [Member] \| TUCSON ELECTRIC POWER COMPANY
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Effect of plan amendment on obligation		1
Effect of Plan Amendment on Future Payments		5
VEBA Trust [Member] \| TUCSON ELECTRIC POWER COMPANY \| Other Retiree Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	$ 3	$ 3	$ 2