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No authoritative reference available. false 2 Utility Plant 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 3 Plant in Service 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 true true false false 4382288000 4382288 false false false 2 true true false false 4147268000 4147268 false false false xbrli:monetaryItemType monetary Period end amount of total gross PPE No authoritative reference available. false 4 Utility Plant under Capital Leases 2 us-gaap_CapitalLeasedAssetsGross us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 583374000 583374 false false false 2 false true false false 720628000 720628 false false false xbrli:monetaryItemType monetary The total gross amount of assets subject to a lease meeting the criteria for capitalization. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 1, 10, 13 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 16 -Subparagraph a(i) false 5 Construction Work in Progress 2 us-gaap_ConstructionInProgressGross us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 152613000 152613 false false false 2 false true false false 144551000 144551 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date of long-lived asset under construction that include construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 true 7 Total Utility Plant 2 us-gaap_PropertyPlantAndEquipmentGross us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 5118275000 5118275 false false false 2 false true false false 5012447000 5012447 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date for long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, physical structures, machinery, vehicles, furniture, computer equipment, construction in progress, and similar items. Amount does not include depreciation. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 false 8 Less Accumulated Depreciation and Amortization 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation us-gaap true credit instant No definition available. false false false false false false false false false false true negated false 1 false true false false -1783411000 -1783411 false false false 2 false true false false -1652296000 -1652296 false false false xbrli:monetaryItemType monetary Period end book value of accumulated depreciation on property, plant and equipment (PPE) that is owned by the regulated operations of the public utility. No authoritative reference available. false 9 Less Accumulated Amortization of Capital Lease Assets 2 uns_AccumulatedAmortizationOfCapitalLeaseAssets uns false credit instant Less Accumulated Amortization of Capital Lease Assets. false false false false false false false false false false true negatedtotal false 1 false true false false -452726000 -452726 false false false 2 false true false false -574437000 -574437 false false false xbrli:monetaryItemType monetary Less Accumulated Amortization of Capital Lease Assets. No authoritative reference available. true 10 Total Utility Plant - Net 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 2882138000 2882138 false false false 2 false true false false 2785714000 2785714 false false false xbrli:monetaryItemType monetary Period end amount of total net PPE No authoritative reference available. true 11 Investments and Other Property 2 uns_InvestmentsAndOtherPropertyAbstract uns false na duration Investments and Other Property. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string Investments and Other Property. false 12 Investments in Lease Debt and Equity 2 uns_NoncurrentPortionOfInvestmentInLeaseDebtAndEquity uns false debit instant Noncurrent portion of Investment in Lease Debt and Equity. false false false false false false false false false false false verboselabel false 1 false true false false 104391000 104391 false false false 2 false true false false 132168000 132168 false false false xbrli:monetaryItemType monetary Noncurrent portion of Investment in Lease Debt and Equity. No authoritative reference available. false 13 Other 2 us-gaap_OtherLongTermInvestments us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 57624000 57624 false false false 2 false true false false 60239000 60239 false false false xbrli:monetaryItemType monetary Other noncurrent investments not otherwise specified in the taxonomy, not including investments in marketable securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph f -Article 7 true 14 Total Investments and Other Property 2 uns_LongTermInvestmentsAndOtherProperty uns false debit instant The total amount of investments and Other Property that are intended to be held for an extended period of time (longer than... false false false false false false false false false false false totallabel false 1 false true false false 162015000 162015 false false false 2 false true false false 192407000 192407 false false false xbrli:monetaryItemType monetary The total amount of investments and Other Property that are intended to be held for an extended period of time (longer than one operating cycle). No authoritative reference available. true 15 Current Assets 2 us-gaap_AssetsCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 16 Cash and Cash Equivalents 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 61409000 61409 false false false 2 false true false false 76922000 76922 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 17 Accounts Receivable - Customer 2 us-gaap_AccountsReceivableGrossCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 78626000 78626 false false false 2 false true false false 80191000 80191 false false false xbrli:monetaryItemType monetary Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 3 -Subparagraph a, b -Article 5 false 18 Unbilled Accounts Receivable 2 uns_UnbilledAccountsReceivableCurrent uns false debit instant Unbilled accounts receivable, current. false false false false false false false false false false false verboselabel false 1 false true false false 63318000 63318 false false false 2 false true false false 53361000 53361 false false false xbrli:monetaryItemType monetary Unbilled accounts receivable, current. No authoritative reference available. false 19 Allowance for Doubtful Accounts 2 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false true negated false 1 false true false false -5944000 -5944 false false false 2 false true false false -5977000 -5977 false false false xbrli:monetaryItemType monetary A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 false 21 Fuel Inventory 2 us-gaap_EnergyRelatedInventory us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 48233000 48233 false false false 2 false true false false 48159000 48159 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of merchandise, goods, commodities, or supplies relating to a source of usable power held for future sale or future use in manufacturing or production process. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 false 22 Materials and Supplies 2 us-gaap_OtherInventorySupplies us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 65539000 65539 false false false 2 false true false false 68633000 68633 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 4 -Paragraph 3 false 23 Derivative Instruments 2 us-gaap_DerivativeAssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 6630000 6630 false false false 2 false true false false 2653000 2653 false false false xbrli:monetaryItemType monetary Fair values as of the balance sheet date for all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments and which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B false 24 Regulatory Assets - Current 2 us-gaap_RegulatoryAssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 58268000 58268 false false false 2 false true false false 41772000 41772 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9, 10 false 25 Deferred Income Taxes - Current 2 us-gaap_DeferredTaxAssetsNetCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 50066000 50066 false false false 2 false true false false 52355000 52355 false false false xbrli:monetaryItemType monetary The current portion of the aggregate tax effects as of the balance sheet date of all future tax deductions arising from temporary differences between tax basis and generally accepted accounting principles basis recognition of assets, liabilities, revenues and expenses, which can only be deducted for tax purposes when permitted under enacted tax laws; after deducting the allocated valuation allowance, if any, to reduce such amount to net realizable value. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. An unrecognized tax benefit that is directly related to a position taken in a tax year that results in a net operating loss carryforward should be presented as a reduction of the related deferred tax asset. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 41, 42, 43 false 26 Investments in Lease Debt 2 us-gaap_HeldToMaturitySecuritiesCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 5462000 5462 false false false 2 false true false false 0 0 false false false xbrli:monetaryItemType monetary This item represents investments in debt securities which are categorized as held-to-maturity and that have scheduled maturities within one year of the balance sheet date or the normal operating cycle, whichever is longer; such investments are measured at amortized cost (carrying value). The held-to-maturity category is for those securities that the Entity has the positive intent and ability to hold until maturity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4, 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 17 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 7, 8, 9, 10, 11 false 27 Other 2 us-gaap_OtherAssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 26360000 26360 false false false 2 false true false false 28236000 28236 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of current assets not separately presented elsewhere in the balance sheet. Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 8 -Article 5 true 28 Total Current Assets 2 us-gaap_AssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 457967000 457967 false false false 2 false true false false 446305000 446305 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 9 -Article 5 true 29 Regulatory and Other Assets 2 us-gaap_AssetsNoncurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 30 Regulatory Assets - Noncurrent 2 us-gaap_RegulatoryAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 150608000 150608 false false false 2 false true false false 147325000 147325 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9, 10 false 31 Derivative Instruments 2 us-gaap_DerivativeAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 6502000 6502 false false false 2 false true false false 4498000 4498 false false false xbrli:monetaryItemType monetary Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments which are expected to exist longer than one year or beyond the normal operating cycle, if longer, net of the effects of master netting arrangements. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B false 32 Other Assets 2 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 23443000 23443 false false false 2 false true false false 24993000 24993 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of noncurrent assets not separately disclosed in the balance sheet due to materiality considerations. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 17 -Article 5 true 33 Total Regulatory and Other Assets 2 uns_TotalNoncurrentRegulatoryAndOtherAssets uns false debit instant Sum of other noncurrent assets other than investments and other property. false false false false false false false false false false false totallabel false 1 false true false false 180553000 180553 false false false 2 false true false false 176816000 176816 false false false xbrli:monetaryItemType monetary Sum of other noncurrent assets other than investments and other property. No authoritative reference available. true 34 Total Assets 2 us-gaap_Assets us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 3682673000 3682673 false false false 2 false true false false 3601242000 3601242 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Concepts (CON) -Number 6 -Paragraph 25 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 18 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 12 -Article 7 true 35 Capitalization 2 us-gaap_CapitalizationLongtermDebtAndEquityAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 36 Common Stock Equity 2 us-gaap_StockholdersEquity us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 772833000 772833 false false false 2 false true false false 750865000 750865 false false false xbrli:monetaryItemType monetary Total of all Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A3 -Appendix A Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 4 -Section E Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 false 37 Capital Lease Obligations 2 us-gaap_CapitalLeaseObligationsNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 439821000 439821 false false false 2 false true false false 488349000 488349 false false false xbrli:monetaryItemType monetary Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid more than one year (or one operating cycle, if longer) after the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 7, 10, 13 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 false 38 Long-Term Debt 2 us-gaap_LongTermDebtNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 1363661000 1363661 false false false 2 false true false false 1307795000 1307795 false false false xbrli:monetaryItemType monetary Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year (current maturities) or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 true 39 Total Capitalization 2 us-gaap_CapitalizationLongtermDebtAndEquity us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 2576315000 2576315 false false false 2 false true false false 2547009000 2547009 false false false xbrli:monetaryItemType monetary This element represents the total consolidated (as applicable) capitalization of the entity which is comprised of its long-term debt and equity instruments. The table may be detailed by subsidiary (legal entity) and include information by type of debt or equity detailed by instrument. No authoritative reference available. true 40 Current Liabilities 2 us-gaap_LiabilitiesCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 41 Current Obligations Under Capital Leases 2 us-gaap_CapitalLeaseObligationsCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 59533000 59533 false false false 2 false true false false 40441000 40441 false false false xbrli:monetaryItemType monetary Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid within one year (or one operating cycle, if longer) of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 7, 10, 13 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Article 5 false 42 Borrowing Under Revolving Credit Facility 2 us-gaap_LinesOfCreditCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 45000000 45000 false false false 2 false true false false 35000000 35000 false false false xbrli:monetaryItemType monetary The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20 -Article 5 false 43 Current Maturities of Long-Term Debt 2 us-gaap_LongTermDebtCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 13000000 13000 false false false 2 false true false false 12195000 12195 false false false xbrli:monetaryItemType monetary Total of the portions of the carrying amounts as of the balance sheet date of long-term debt, which may include notes payable, bonds payable, debentures, mortgage loans, and commercial paper, which are scheduled to be repaid within one year or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Article 5 false 44 Accounts Payable - Trade 2 us-gaap_AccountsPayableTradeCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 107800000 107800 false false false 2 false true false false 98990000 98990 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of obligations incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 false 46 Interest Accrued 2 us-gaap_InterestPayableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 27442000 27442 false false false 2 false true false false 41396000 41396 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 47 Accrued Taxes Other Than Income Taxes 2 us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 38575000 38575 false false false 2 false true false false 36698000 36698 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 10 -Section A -Paragraph 16 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 48 Accrued Employee Expenses 2 us-gaap_EmployeeRelatedLiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 24161000 24161 false false false 2 false true false false 27545000 27545 false false false xbrli:monetaryItemType monetary Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 49 Customer Deposits 2 us-gaap_CustomerDepositsCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 27879000 27879 false false false 2 false true false false 25978000 25978 false false false xbrli:monetaryItemType monetary The current portion, due within one year or the normal operating cycle, if longer, of money or property received from customers which is either to be returned upon satisfactory contract completion or applied to customer receivables in accordance with the terms of the contract or the understandings. No authoritative reference available. false 50 Regulatory Liabilities - Current 2 us-gaap_RegulatoryLiabilityCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 47378000 47378 false false false 2 false true false false 42229000 42229 false false false xbrli:monetaryItemType monetary The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 11 false 51 Derivative Instruments 2 us-gaap_DerivativeLiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 33248000 33248 false false false 2 false true false false 21186000 21186 false false false xbrli:monetaryItemType monetary Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be extinguished or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 false 52 Other 2 us-gaap_OtherLiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 8244000 8244 false false false 2 false true false false 4038000 4038 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of current obligations not separately disclosed in the balance sheet due to materiality considerations. Current liabilities are expected to be paid within one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 8 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 6 -Paragraph 15 true 53 Total Current Liabilities 2 us-gaap_LiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 432260000 432260 false false false 2 false true false false 385696000 385696 false false false xbrli:monetaryItemType monetary Total obligations incurred as part of normal operations that are expected to be paid during the following twelve months or within one business cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 21 -Article 5 true 54 Deferred Credits and Other Liabilities 2 us-gaap_LiabilitiesNoncurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 55 Deferred Income Taxes - Noncurrent 2 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 244441000 244441 false false false 2 false true false false 227199000 227199 false false false xbrli:monetaryItemType monetary Represents the noncurrent portion of deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A noncurrent taxable temporary difference is a difference between the tax basis and the carrying amount of a noncurrent asset or liability in the financial statements prepared in accordance with generally accepted accounting principles. In a classified statement of financial position, an enterprise shall separate deferred tax liabilities and assets into a current amount and a noncurrent amount. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 41, 42 false 56 Regulatory Liabilities - Noncurrent 2 us-gaap_RegulatoryLiabilityNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 189159000 189159 false false false 2 false true false false 211891000 211891 false false false xbrli:monetaryItemType monetary The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 11 false 57 Derivative Instruments 2 us-gaap_DerivativeLiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 23481000 23481 false false false 2 false true false false 19489000 19489 false false false xbrli:monetaryItemType monetary Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be extinguished or otherwise disposed of after one year or beyond the normal operating cycle, if longer, net of the effects of master netting arrangements. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B false 58 Pension and Other Postretirement Benefits 2 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 127641000 127641 false false false 2 false true false false 123476000 123476 false false false xbrli:monetaryItemType monetary This represents the noncurrent liability for underfunded plans recognized in the balance sheet that is associated with the defined benefit pension plans and other postretirement defined benefit plans. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph c Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 6 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 3 false 59 Other 2 us-gaap_OtherLiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 89376000 89376 false false false 2 false true false false 86482000 86482 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of noncurrent obligations not separately disclosed in the balance sheet due to materiality considerations. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 24 -Article 5 true 60 Total Deferred Credits and Other Liabilities 2 us-gaap_LiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 674098000 674098 false false false 2 false true false false 668537000 668537 false false false xbrli:monetaryItemType monetary Total obligations incurred as part of normal operations that is expected to be repaid beyond the following twelve months or one business cycle. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22, 23, 24, 25, 26, 27 -Article 5 true 61 Commitments and Contingencies (Note 6) 2 us-gaap_CommitmentsAndContingencies2009 us-gaap true na duration No definition available. false false false false false false false false false false false totallabel false 1 false false false false 0 0   false false false 2 false false false false 0 0   false false false xbrli:stringItemType string Represents the caption on the face of the balance sheet to indicate that the entity has entered into (1) purchase or supply arrangements that will require expending a portion of its resources to meet the terms thereof, and (2) is exposed to potential losses or, less frequently, gains, arising from (a) possible claims against a company's resources due to future performance under contract terms, and (b) possible losses or likely gains from uncertainties that will ultimately be resolved when one or more future events that are deemed likely to occur do occur or fail to occur. This caption alerts the reader that one or more notes to the financial statements disclose pertinent information about the entity's commitments and contingencies. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 5 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 25 -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 17 -Article 9 false 62 Total Capitalization and Other Liabilities 2 us-gaap_LiabilitiesAndStockholdersEquity us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 3682673000 3682673 false false false 2 false true false false 3601242000 3601242 false false false xbrli:monetaryItemType monetary Total of all Liabilities and Stockholders' Equity items. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 32 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 25 -Article 7 true 63 TUCSON ELECTRIC POWER COMPANY 0 na true na na No definition available. false true false false false false false false false false false http://uns.com/role/balancesheets false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false false 5 USD true false false false us-gaap_SubsidiariesMember dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 6 USD true false false false us-gaap_SubsidiariesMember dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 7 USD true false false false us-gaap_SubsidiariesMember dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ false 8 USD true false false false us-gaap_SubsidiariesMember dei_LegalEntityAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SubsidiariesMember dei_LegalEntityAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ na No definition available. No authoritative reference available. false 64 Utility Plant 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 65 Plant in Service 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentPlantInService us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 3800096000 3800096 false false false 2 false true false false 3584308000 3584308 false false false xbrli:monetaryItemType monetary Period end amount of total gross PPE No authoritative reference available. false 66 Utility Plant under Capital Leases 2 us-gaap_CapitalLeasedAssetsGross us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 582669000 582669 false false false 2 false true false false 719922000 719922 false false false xbrli:monetaryItemType monetary The total gross amount of assets subject to a lease meeting the criteria for capitalization. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 1, 10, 13 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 16 -Subparagraph a(i) false 68 Construction Work in Progress 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 121963000 121963 false false false 2 false true false false 113390000 113390 false false false xbrli:monetaryItemType monetary Period end amount of construction work in progress in public utility No authoritative reference available. true 69 Total Utility Plant 2 us-gaap_PropertyPlantAndEquipmentGross us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 4504728000 4504728 false false false 2 false true false false 4417620000 4417620 false false false xbrli:monetaryItemType monetary Carrying amount at the balance sheet date for long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, physical structures, machinery, vehicles, furniture, computer equipment, construction in progress, and similar items. Amount does not include depreciation. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 false 70 Less Accumulated Depreciation and Amortization 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation us-gaap true credit instant No definition available. false false false false false false false false false false true negated false 1 false true false false -1702517000 -1702517 false false false 2 false true false false -1582442000 -1582442 false false false xbrli:monetaryItemType monetary Period end book value of accumulated depreciation on property, plant and equipment (PPE) that is owned by the regulated operations of the public utility. No authoritative reference available. false 71 Less Accumulated Amortization of Capital Lease Assets 2 uns_AccumulatedAmortizationOfCapitalLeaseAssets uns false credit instant Less Accumulated Amortization of Capital Lease Assets. false false false false false false false false false false true negatedtotal false 1 false true false false -452097000 -452097 false false false 2 false true false false -573853000 -573853 false false false xbrli:monetaryItemType monetary Less Accumulated Amortization of Capital Lease Assets. No authoritative reference available. true 72 Total Utility Plant - Net 2 us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 2350114000 2350114 false false false 2 false true false false 2261325000 2261325 false false false xbrli:monetaryItemType monetary Period end amount of total net PPE No authoritative reference available. true 73 Investments and Other Property 2 uns_InvestmentsAndOtherPropertyAbstract uns false na duration Investments and Other Property. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string Investments and Other Property. false 74 Investments in Lease Debt and Equity 2 uns_NoncurrentPortionOfInvestmentInLeaseDebtAndEquity uns false debit instant Noncurrent portion of Investment in Lease Debt and Equity. false false false false false false false false false false false verboselabel false 1 false true false false 104391000 104391 false false false 2 false true false false 132168000 132168 false false false xbrli:monetaryItemType monetary Noncurrent portion of Investment in Lease Debt and Equity. No authoritative reference available. false 75 Other 2 us-gaap_OtherLongTermInvestments us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 33709000 33709 false false false 2 false true false false 31813000 31813 false false false xbrli:monetaryItemType monetary Other noncurrent investments not otherwise specified in the taxonomy, not including investments in marketable securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph f -Article 7 true 76 Total Investments and Other Property 2 uns_LongTermInvestmentsAndOtherProperty uns false debit instant The total amount of investments and Other Property that are intended to be held for an extended period of time (longer than... false false false false false false false false false false false totallabel false 1 false true false false 138100000 138100 false false false 2 false true false false 163981000 163981 false false false xbrli:monetaryItemType monetary The total amount of investments and Other Property that are intended to be held for an extended period of time (longer than one operating cycle). No authoritative reference available. true 77 Current Assets 2 us-gaap_AssetsCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 78 Cash and Cash Equivalents 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 18655000 18655 false false false 2 false true false false 22418000 22418 false false false xbrli:monetaryItemType monetary Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 1 -Article 5 false 79 Accounts Receivable - Customer 2 us-gaap_AccountsReceivableGrossCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 63627000 63627 false false false 2 false true false false 62508000 62508 false false false xbrli:monetaryItemType monetary Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 3 -Subparagraph a, b -Article 5 false 80 Unbilled Accounts Receivable 2 uns_UnbilledAccountsReceivableCurrent uns false debit instant Unbilled accounts receivable, current. false false false false false false false false false false false verboselabel false 1 false true false false 51562000 51562 false false false 2 false true false false 32368000 32368 false false false xbrli:monetaryItemType monetary Unbilled accounts receivable, current. No authoritative reference available. false 81 Allowance for Doubtful Accounts 2 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false true negated false 1 false true false false -4048000 -4048 false false false 2 false true false false -3806000 -3806 false false false xbrli:monetaryItemType monetary A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 false 82 Accounts Receivable - Due from Affiliates 2 us-gaap_AccountsReceivableRelatedPartiesCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 4718000 4718 false false false 2 false true false false 5218000 5218 false false false xbrli:monetaryItemType monetary Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph k -Subparagraph 1 -Article 4 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 57 -Paragraph 2 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph a -Article 5 false 83 Fuel Inventory 2 us-gaap_EnergyRelatedInventory us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 48223000 48223 false false false 2 false true false false 48149000 48149 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of merchandise, goods, commodities, or supplies relating to a source of usable power held for future sale or future use in manufacturing or production process. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 false 84 Materials and Supplies 2 us-gaap_OtherInventorySupplies us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 54740000 54740 false false false 2 false true false false 56712000 56712 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 4 -Paragraph 3 false 85 Derivative Instruments 2 us-gaap_DerivativeAssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 2599000 2599 false false false 2 false true false false 5043000 5043 false false false xbrli:monetaryItemType monetary Fair values as of the balance sheet date for all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments and which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B false 86 Regulatory Assets - Current 2 us-gaap_RegulatoryAssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 33594000 33594 false false false 2 false true false false 27026000 27026 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9, 10 false 87 Deferred Income Taxes - Current 2 us-gaap_DeferredTaxAssetsNetCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 50319000 50319 false false false 2 false true false false 50789000 50789 false false false xbrli:monetaryItemType monetary The current portion of the aggregate tax effects as of the balance sheet date of all future tax deductions arising from temporary differences between tax basis and generally accepted accounting principles basis recognition of assets, liabilities, revenues and expenses, which can only be deducted for tax purposes when permitted under enacted tax laws; after deducting the allocated valuation allowance, if any, to reduce such amount to net realizable value. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. An unrecognized tax benefit that is directly related to a position taken in a tax year that results in a net operating loss carryforward should be presented as a reduction of the related deferred tax asset. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 41, 42, 43 false 88 Investments in Lease Debt 2 us-gaap_HeldToMaturitySecuritiesCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 5462000 5462 false false false 2 false true false false 0 0 false false false xbrli:monetaryItemType monetary This item represents investments in debt securities which are categorized as held-to-maturity and that have scheduled maturities within one year of the balance sheet date or the normal operating cycle, whichever is longer; such investments are measured at amortized cost (carrying value). The held-to-maturity category is for those securities that the Entity has the positive intent and ability to hold until maturity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4, 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 17 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 7, 8, 9, 10, 11 false 89 Other 2 us-gaap_OtherAssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 22333000 22333 false false false 2 false true false false 24362000 24362 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of current assets not separately presented elsewhere in the balance sheet. Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 8 -Article 5 true 90 Total Current Assets 2 us-gaap_AssetsCurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 351784000 351784 false false false 2 false true false false 330787000 330787 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 9 -Article 5 true 91 Regulatory and Other Assets 2 us-gaap_AssetsNoncurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 92 Regulatory Assets - Noncurrent 2 us-gaap_RegulatoryAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 140102000 140102 false false false 2 false true false false 137147000 137147 false false false xbrli:monetaryItemType monetary Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9, 10 false 93 Derivative Instruments 2 us-gaap_DerivativeAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 1777000 1777 false false false 2 false true false false 1075000 1075 false false false xbrli:monetaryItemType monetary Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments which are expected to exist longer than one year or beyond the normal operating cycle, if longer, net of the effects of master netting arrangements. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 4 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B false 94 Other Assets 2 us-gaap_OtherAssetsNoncurrent us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 19102000 19102 false false false 2 false true false false 19984000 19984 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of noncurrent assets not separately disclosed in the balance sheet due to materiality considerations. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 17 -Article 5 true 95 Total Regulatory and Other Assets 2 uns_TotalNoncurrentRegulatoryAndOtherAssets uns false debit instant Sum of other noncurrent assets other than investments and other property. false false false false false false false false false false false totallabel false 1 false true false false 160981000 160981 false false false 2 false true false false 158206000 158206 false false false xbrli:monetaryItemType monetary Sum of other noncurrent assets other than investments and other property. No authoritative reference available. true 96 Total Assets 2 us-gaap_Assets us-gaap true debit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 3000979000 3000979 false false false 2 false true false false 2914299000 2914299 false false false xbrli:monetaryItemType monetary Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Concepts (CON) -Number 6 -Paragraph 25 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 18 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 12 -Article 7 true 97 Capitalization 2 us-gaap_CapitalizationLongtermDebtAndEquityAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 98 Common Stock Equity 2 us-gaap_StockholdersEquity us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 692729000 692729 false false false 2 false true false false 643144000 643144 false false false xbrli:monetaryItemType monetary Total of all Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A3 -Appendix A Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 4 -Section E Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 false 99 Capital Lease Obligations 2 us-gaap_CapitalLeaseObligationsNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 439821000 439821 false false false 2 false true false false 488311000 488311 false false false xbrli:monetaryItemType monetary Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid more than one year (or one operating cycle, if longer) after the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 7, 10, 13 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 false 100 Long-Term Debt 2 us-gaap_LongTermDebtNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 933615000 933615 false false false 2 false true false false 903615000 903615 false false false xbrli:monetaryItemType monetary Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year (current maturities) or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 true 101 Total Capitalization 2 us-gaap_CapitalizationLongtermDebtAndEquity us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 2066165000 2066165 false false false 2 false true false false 2035070000 2035070 false false false xbrli:monetaryItemType monetary This element represents the total consolidated (as applicable) capitalization of the entity which is comprised of its long-term debt and equity instruments. The table may be detailed by subsidiary (legal entity) and include information by type of debt or equity detailed by instrument. No authoritative reference available. true 102 Current Liabilities 2 us-gaap_LiabilitiesCurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 103 Current Obligations Under Capital Leases 2 us-gaap_CapitalLeaseObligationsCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 59440000 59440 false false false 2 false true false false 40332000 40332 false false false xbrli:monetaryItemType monetary Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid within one year (or one operating cycle, if longer) of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 13 -Paragraph 7, 10, 13 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Article 5 false 104 Borrowing Under Revolving Credit Facility 2 us-gaap_LinesOfCreditCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 45000000 45000 false false false 2 false true false false 35000000 35000 false false false xbrli:monetaryItemType monetary The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20 -Article 5 false 106 Accounts Payable - Trade 2 us-gaap_AccountsPayableTradeCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 91606000 91606 false false false 2 false true false false 71328000 71328 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of obligations incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 false 107 Accounts Payable - Due to Affiliates 2 us-gaap_AccountsPayableRelatedPartiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 3668000 3668 false false false 2 false true false false 3694000 3694 false false false xbrli:monetaryItemType monetary Amount for accounts payable to related parties. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 57 -Paragraph 2 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph k -Subparagraph 1 -Article 4 false 108 Interest Accrued 2 us-gaap_InterestPayableCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 20030000 20030 false false false 2 false true false false 33970000 33970 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 109 Accrued Taxes Other Than Income Taxes 2 us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 31770000 31770 false false false 2 false true false false 28404000 28404 false false false xbrli:monetaryItemType monetary Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 10 -Section A -Paragraph 16 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 110 Accrued Employee Expenses 2 us-gaap_EmployeeRelatedLiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 21371000 21371 false false false 2 false true false false 24409000 24409 false false false xbrli:monetaryItemType monetary Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 false 111 Customer Deposits 2 us-gaap_CustomerDepositsCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 19518000 19518 false false false 2 false true false false 18125000 18125 false false false xbrli:monetaryItemType monetary The current portion, due within one year or the normal operating cycle, if longer, of money or property received from customers which is either to be returned upon satisfactory contract completion or applied to customer receivables in accordance with the terms of the contract or the understandings. No authoritative reference available. false 112 Regulatory Liabilities - Current 2 us-gaap_RegulatoryLiabilityCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 40262000 40262 false false false 2 false true false false 26639000 26639 false false false xbrli:monetaryItemType monetary The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 11 false 113 Derivative Instruments 2 us-gaap_DerivativeLiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 8657000 8657 false false false 2 false true false false 9434000 9434 false false false xbrli:monetaryItemType monetary Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be extinguished or otherwise disposed of within a year or the normal operating cycle, if longer, net of the effects of master netting arrangements. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10A, 10B Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 4, 17 false 114 Other 2 us-gaap_OtherLiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 10543000 10543 false false false 2 false true false false 1445000 1445 false false false xbrli:monetaryItemType monetary Aggregate carrying amount, as of the balance sheet date, of current obligations not separately disclosed in the balance sheet due to materiality considerations. Current liabilities are expected to be paid within one year (or the normal operating cycle, if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 3 -Section A -Paragraph 8 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 6 -Paragraph 15 true 115 Total Current Liabilities 2 us-gaap_LiabilitiesCurrent us-gaap true credit instant No definition available. false false false false false false false false false false false totallabel false 1 false true false false 351865000 351865 false false false 2 false true false false 292780000 292780 false false false xbrli:monetaryItemType monetary Total obligations incurred as part of normal operations that are expected to be paid during the following twelve months or within one business cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 21 -Article 5 true 116 Deferred Credits and Other Liabilities 2 us-gaap_LiabilitiesNoncurrentAbstract us-gaap true na duration No definition available. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false xbrli:stringItemType string No definition available. false 117 Deferred Income Taxes - Noncurrent 2 us-gaap_DeferredTaxLiabilitiesNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 230241000 230241 false false false 2 false true false false 217316000 217316 false false false xbrli:monetaryItemType monetary Represents the noncurrent portion of deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A noncurrent taxable temporary difference is a difference between the tax basis and the carrying amount of a noncurrent asset or liability in the financial statements prepared in accordance with generally accepted accounting principles. In a classified statement of financial position, an enterprise shall separate deferred tax liabilities and assets into a current amount and a noncurrent amount. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 41, 42 false 118 Regulatory Liabilities - Noncurrent 2 us-gaap_RegulatoryLiabilityNoncurrent us-gaap true credit instant No definition available. false false false false false false false false false false false verboselabel false 1 false true false false 155587000 155587 false false false 2 false true false false 179478000 179478 false false false xbrli:monetaryItemType monetary The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. 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