Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative [Table] Derivative [Table] Derivative Instruments, Gain (Loss) by Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging [Member] Cash Flow Hedging [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Questar Pipeline [Member] Questar Pipeline [Member] Questar Pipeline Company operates interstate natural gas pipelines and storage facilities in the western United States and provides other energy services. Derivative, by Nature [Axis] Derivative, by Nature [Axis] Derivative, Name [Domain] Derivative, Name [Domain] Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member] Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member] An agreement to exchange two different, defined streams of interest beginning on a specified date in the future. Derivative [Line Items] Derivative [Line Items] Notional amount Derivative, Notional Amount Debt Instrument, Face Amount Debt Instrument, Face Amount Interest payment for terminated derivative instrument Derivative, Loss on Derivative Life of long-term debt associated with cash flow hedges Life of Long-Term Debt Associated with Cash Flow Hedges Life of Long-Term Debt Associated with Cash Flow Hedges (in years) Date Through Which Reclassifications Into Earnings From AOCI Will Take Place Date Through Which Reclassifications Into Earnings From AOCI Will Take Place Date Through Which Reclassifications Into Earnings From AOCI Will Take Place Pre-tax net losses expected to be reclassified from AOCI to Consolidated statement of income Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Reclassification from accumulated OCI to income, time to transfer Reclassification from accumulated OCI to income, estimated time to transfer The time period estimated for the anticipated transfer of gains (losses), net from accumulated other comprehensive income into earnings. Derivative Assets (Liabilities), at Fair Value, Net Derivative Assets (Liabilities), at Fair Value, Net Earnings Per Share [Abstract] Weighted-average basic common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Potential number of shares issuable under the Company's LTSIP (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted-average diluted common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Fair Value Disclosures [Abstract] Abandonment and impairment Asset Impairment Charges Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Wexpro [Member] Wexpro [Member] Wexpro Company develops and produces natural gas from cost-of-service reserves for Questar Gas. Questar Gas [Member] Questar Gas [Member] Questar Gas Company provides retail natural gas distribution services in Utah, Wyoming and Idaho. Questar Pipeline [Member] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Amount [Member] Reported Value Measurement [Member] Estimated Fair Value [Member] Estimate of Fair Value Measurement [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring [Member] Fair Value, Measurements, Recurring [Member] Fair Value Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Financial assets [Abstract] Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Cash and cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Notes receivable from Questar Notes Receivable Affiliated Fair Value Disclosure This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. An amount representing an agreement for an unconditional promise by the maker to pay the affiliated Company (holder) a definite sum of money at a future date(s). Long-term investment Investments, Fair Value Disclosure Financial liabilities [Abstract] Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Checks outstanding in excess of cash balances Checks Outstanding In Excess Of Cash Balances Fair Value Disclosure This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents checks outstanding in excess of cash balances as of the balance sheet date. Notes payable to Questar Notes Payable Affiliated Fair Value Disclosure This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents affiliated notes payable as of the balance sheet date. Short-term debt Short-term Debt, Fair Value Long-term debt, including current portion Long-term Debt, Fair Value Wexpro Impairment [Abstract] Wexpro Impairment [Abstract] Asset Impairments Wexpro Impairment [Text Block] Wexpro Impairment [Text Block] Asset Retirement Obligation [Abstract] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] AROs at beginning of year Asset Retirement Obligations, Noncurrent Accretion Asset Retirement Obligation, Accretion Expense Liabilities incurred Asset Retirement Obligation, Liabilities Incurred Revisions in estimated cash flows Asset Retirement Obligation, Revision of Estimate Liabilities settled Asset Retirement Obligation, Liabilities Settled AROs at end of period Statement of Comprehensive Income [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Pension and OPB Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Interest rate cash flow hedges Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Commodity cash flow hedges Accumulated Net Gain (Loss) from Designated or Qualifying Commodity Cash Flow Hedges [Member] Changes to accumulated comprehensive income resulting from gains and losses from derivative instruments designated and qualifying as the effective portion of commodity cash flow hedges. A commodity cash flow hedge is a hedge of the exposure to variability in the commodity cash flows of a recognized asset or liability or a forecasted transaction that is attributable to a particular risk. Long-term investment Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Statement [Line Items] Statement [Line Items] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] AOCI at beginning of period Accumulated Other Comprehensive Income (Loss), Net of Tax OCI before reclassifications Other Comprehensive Income (Loss), before Reclassifications, before Tax Reclassified from AOCI Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Income taxes Other Comprehensive Income (Loss), Tax [Abstract] Reclassified from AOCI Reclassifications from Accumulated Other Comprehensive Income, Current Period, Tax Reclassifications from Accumulated Other Comprehensive Income, Current Period, Tax Total income taxes Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Net other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent AOCI at end of period Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Statement, Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Net income Net Income (Loss) Attributable to Parent Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax [Abstract] Pension and other postretirement benefits Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax Interest rate cash flow hedge amortization Other comprehensive income unrealized gain loss on interest rate cash flow hedges Pre tax change in accumulated gains and losses from interest rate cash flow hedge. A cash flow hedge is a hedge of the exposure to variability in the cash flows of a recognized asset or liability or a forecasted transaction that is attributable to a particular risk. Includes an entity's share of an equity investee's increase (decrease) in deferred hedging gains or losses. Commodity cash flow hedge Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax Income taxes COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Attributable to Parent Accumulated Other Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Compensation and Retirement Disclosure [Abstract] Employee Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Nature of Business Nature Of Operations [Policy Text Block] Describes the nature of an entity's business, the major products or services it sells or provides and its principal markets, including the locations of those markets. If the entity operates in more than one business, the disclosure also indicates the relative importance of its operations in each business and the basis for the determination (for example, assets, revenues, or earnings). Disclosures about the nature of operations need not be quantified; relative importance could be conveyed by use of terms such as "predominately", "about equally", or "major and other". This element is also referred to as "Business Description". Investment in Unconsolidated Affiliate Equity Method Investments, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Comprehensive Income - Questar Comprehensive Income [Policy Text Block] Comprehensive Income [Policy Text Block] Comprehensive Income - Questar Pipeline Comprehensive Income Note Policy - Questar Pipeline [Text Block] This element may include the following: 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income. Components of comprehensive income include: (1) foreign currency translation adjustments; (2) gains and losses on foreign currency transactions that are designated as, and are effective as, economic hedges of a net investment in a foreign entity; (3) gains and losses on intercompany foreign currency transactions that are of a long-term-investment nature, when the entities to the transaction are consolidated, combined, or accounted for by the equity method in the reporting enterprise's financial statements; (4) change in the market value of a futures contract that qualifies as a hedge of an asset reported at fair value; (5) unrealized holding gains and losses on available-for-sale securities and that resulting from transfers of debt securities from the held-to-maturity category to the available-for-sale category; (6) a net loss recognized as an additional pension liability not yet recognized as net periodic pension cost; and (7) the net gain or loss and net prior service cost or credit for pension plans and other postretirement benefit plans. Asset Retirement Obligations Asset Retirement Obligations Policy Text Block Describes an entity's accounting policy for determining amounts to accrue and charge against earnings so as to satisfy legal obligations associated with the retirement (through sale, abandonment, recycling, or disposal in some other manner) of a tangible long-lived asset that result from the acquisition, construction, or development and (or) the normal operation of a long-lived asset. This accounting policy disclosure excludes obligations arising 1) in connection with leased property, whether imposed by a lease agreement or by a party other than the lessor, that meet the definition of either minimum lease payments or contingent rentals; 2) solely from a plan to sell or otherwise dispose of a long-lived asset and 3) from certain environmental remediation liabilities. Business Segments Segment Reporting Policy Text Block This element may be used to describe the disclosure of reporting segments. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10% or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments. Contingencies Commitments and Contingencies, Policy [Policy Text Block] Questar Gas [Member] Fair Value, by Balance Sheet Grouping Fair Value, by Balance Sheet Grouping [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Contingencies Contingencies Disclosure [Text Block] Nature of Business Nature of Operations [Text Block] Cost of sales detail Cost of sales detail [Table Text Block] Cost of sales detail [Table Text Block] Segment Reporting [Abstract] Operations by Line of Business Segment Reporting Disclosure [Text Block] Earnings Per Share Earnings Per Share [Text Block] Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Current Assets Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Notes receivable from Questar Notes Receivable, Related Parties, Current Accounts receivable, net Accounts Receivable, Net, Current Unbilled gas accounts receivable Unbilled Contracts Receivable Accounts receivable from affiliates Accounts Receivable, Related Parties, Current Gas stored underground Energy Related Inventory, Gas Stored Underground Materials and supplies Other Inventory, Supplies, Gross Current regulatory assets Regulatory Assets, Current Prepaid expenses and other Prepaid Expense, Current Total Current Assets Assets, Current Property, Plant and Equipment Property, Plant and Equipment, Gross Accumulated depreciation, depletion and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Net Property, Plant and Equipment Property, Plant and Equipment, Net Investment in unconsolidated affiliate Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Noncurrent regulatory assets Regulatory Assets, Noncurrent Noncurrent regulatory and other assets Regulatory and other noncurrent assets The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. Also includes 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). Other noncurrent assets Other Assets, Noncurrent TOTAL ASSETS Assets LIABILITIES AND COMMON SHAREHOLDERS' EQUITY Liabilities and Equity [Abstract] Current Liabilities Liabilities, Current [Abstract] Checks outstanding in excess of cash balances Bank Overdrafts Short-term debt Short-term Debt Notes payable to Questar Notes Payable, Related Parties, Current Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities, Current Accounts payable to affiliates Accounts Payable, Related Parties, Current Customer advances Customer Advances, Current Current regulatory liabilities Regulatory Liability, Current Current portion of long-term debt and capital lease obligation Long-term Debt and Capital Lease Obligations, Current Current portion of long-term debt Long-term Debt, Current Maturities Total Current Liabilities Liabilities, Current Long-term debt and capital lease obligation, less current portion Long-term Debt and Capital Lease Obligations Long-term debt, less current portion Long-term Debt, Excluding Current Maturities Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Asset retirement obligations Defined benefit pension plan and other postretirement benefits Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Noncurrent regulatory liabilities Regulatory Liability, Noncurrent Customer contributions in aid of construction Contributions in Aid of Construction Other noncurrent liabilities Other Liabilities, Noncurrent Noncurrent regulatory and other liabilities Regulatory and other noncurrent liabilities The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. Also, includes the 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). COMMON SHAREHOLDERS' EQUITY Stockholders' Equity Attributable to Parent [Abstract] Common stock Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive (loss) Total Common Shareholders' Equity Stockholders' Equity Attributable to Parent TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY Liabilities and Equity Schedule of Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Ownership percentage in unconsolidated affiliate (in hundredths) Equity Method Investment, Ownership Percentage Cost of Sales [Abstract] Cost of Goods and Services Sold [Abstract] Gas purchases Gas purchases Cost of natural gas purchased from third parties. Excludes transportation, gathering and storage costs. Operator service fee Operator service fee Operator service fee charged to Questar Gas by Wexpro for the development and operation of cost-of-service natural gas reserves. Transportation and storage Transportation and storage Natural gas transportation and storage costs, predominantly consists of amounts charged to Questar Gas by Questar Pipeline. Gathering Gathering Natural gas gathering costs charged by third parties. Royalties Royalties Portion of gas purchase costs that represents amounts paid to Wexpro to reimburse them for royalties on natural gas and other products. Royalties are billed to Questar Gas by Wexpro separate from the operator service fee. Storage (injection) withdrawal, net Storage (injection) withdrawal, net Represents the offset to inventory entries when natural gas is physically injected into or withdrawn from storage facilities. As inventory is increased (debited), this offset component of gas costs is credited and vice versa. Purchased-gas account adjustment Increase (Decrease) in Deferred Gas Cost Other Other gas cost components Other miscellaneous components of Questar Gas cost of natural gas sold. Total Questar Gas cost of natural gas sold Cost of Domestic Regulated Gas Revenue Elimination of Questar Gas cost of natural gas sold - affiliated companies Cost of Domestic Regulated Gas Revenue Affiliated Companies Cost of oil and gas purchased from and transported by affiliated companies during the reporting period. Total Questar Gas cost of natural gas sold - unaffiliated parties Cost of Purchased Oil and Gas Unaffiliated Parties Cost of oil and gas purchased from unaffiliated parties during the reporting period. Questar Pipeline cost of sales Cost of Goods and Services Sold Other cost of sales Cost of Natural Gas Purchases Total cost of sales Cost of Goods Sold, Oil and Gas Changes in AROs Schedule of Asset Retirement Obligations [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Intersegment Eliminations [Member] Intersegment Eliminations [Member] Segment Reporting Information, by Segment [Axis] Segments [Axis] Reporting Segment [Domain] Segments [Domain] Wexpro [Member] Corporate and Other [Member] Questar Corp [Member] [Parent Company] Questar Corporation (Questar or the Company) is a Rockies-based integrated natural gas company. Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Number of principal complementary lines of business Number Of Lines Of Business The number of complementary lines of business the company conducts. Revenues by Line of Business Revenues Operating Income (Loss) Operating Income (Loss) Net Income (Loss) Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Schedule of Defined Benefit Plans Disclosures Schedule of Defined Benefit Plans Disclosures [Table Text Block] Income Statement [Abstract] REVENUES Revenues [Abstract] Questar Gas / Revenues Gas Domestic Regulated Revenue Distribution Revenue derived from the regulated (by a federal, state, or local government or agency) distribution of natural gas. Wexpro Natural Gas Production Revenue Questar Pipeline / Revenues from unaffiliated customers Gas Domestic Regulated Revenue Transmission Revenue derived from the regulated (by a federal, state, or local government or agency) transmission of natural gas. Other Other Revenue, Net Revenues from affiliated companies Gas Domestic Regulated Revenue Transmission Affiliated Companies Revenue derived from the regulated (by a federal, state, or local government or agency) transmission of natural gas to affiliated companies. Total Revenues OPERATING EXPENSES Operating Expenses [Abstract] Cost of natural gas sold (excluding operating expenses shown separately) Cost of sales (excluding operating expenses shown separately) Operating and maintenance Cost of Property Repairs and Maintenance General and administrative General and Administrative Expense Pension settlement costs Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements Merger and restructuring costs Restructuring Charges Production and other taxes Taxes, Miscellaneous Depreciation, depletion and amortization Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization Utilities Operating Expense, Depreciation and Amortization Other taxes Taxes, Other Cost of sales (excluding operating expenses shown separately) Total Operating Expenses Operating Expenses Net gain (loss) from asset sales Gain (Loss) on Disposition of Property Plant Equipment OPERATING INCOME Interest and other income Investment Income, Nonoperating Income from unconsolidated affiliate Income (Loss) from Equity Method Investments Interest expense Interest Expense INCOME BEFORE INCOME TAXES Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest Income taxes Income Tax Expense (Benefit) NET INCOME Earnings Per Common Share Basic (usd per share) Earnings Per Share, Basic Diluted (usd per share) Earnings Per Share, Diluted Weighted-average common shares outstanding Weighted Average Number of Shares Outstanding, Diluted [Abstract] Used in basic calculation (in shares) Used in diluted calculation (in shares) Dividends per common share (usd per share) Common Stock, Dividends, Per Share, Cash Paid Business Combinations [Abstract] Proposed Merger with Dominion Business Combination Disclosure [Text Block] Recent Accounting Developments [Abstract] Recent Accounting Developments [Abstract] Recent Accounting Developments New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Basis of Presentation of Interim Financial Statements Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plans Disclosures, Defined Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans [Domain] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Qualified and nonqualified pension plans [Member] United States Pension Plan of US Entity [Member] Postretirement benefits plan [Member] United States Postretirement Benefit Plan of US Entity [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return on Plan Assets Prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Recognized net actuarial loss Defined Benefit Plan, Actuarial Gain (Loss) Pension settlement costs Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments Recognized net actuarial loss Defined Benefit Plan, Amortization of Gains (Losses) Accretion of regulatory liability Defined Benefit Plan Accretion Of Regulatory Liability A periodic charge recognizing amounts collected in rates in excess of actual postretirement expenses. Net benefit cost Defined Benefit Plan, Net Periodic Benefit Cost Estimated qualified pension plan cost for current fiscal year Qualified Defined Benefit Pension Plan Estimated Cost In Current Fiscal Year The employer's best estimate of qualified pension plan cost for the current fiscal year. Since the company plans to fund the qualified retirement plan in amounts approximately equal to the yearly expense, this element also represents estimated employer contributions expected to be paid for the current fiscal year. Estimated nonqualified pension plan cost for current fiscal year Nonqualified Defined Benefit Pension Plan Estimated Cost In Current Fiscal Year The employer's best estimate of nonqualified pension plan cost for the current fiscal year. The nonqualified pension plan is unfunded. Estimated postretirement benefits cost for current fiscal year, before accretion of regulatory liability Defined Benefit Postretirement Benefits Plan Estimated Cost In Current Fiscal Year The employer's best estimate of postretirement benefits cost for the current fiscal year, before accretion of regulatory liability. Asset Retirement Obligations Asset Retirement Obligation Disclosure [Text Block] Statement of Cash Flows [Abstract] OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation, depletion and amortization Depreciation, Depletion and Amortization Depreciation and amortization Depreciation, Amortization and Accretion, Net Deferred income taxes Deferred Income Tax Expense (Benefit) Share-based compensation Share-based Compensation Net (gain) from asset sales (Income) from unconsolidated affiliate Distributions from unconsolidated affiliate and other Proceeds from Equity Method Investment, Dividends or Distributions Changes in operating assets and liabilities Increase (Decrease) in Operating Capital NET CASH PROVIDED BY OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Property, plant and equipment purchased Payments to Acquire Property, Plant, and Equipment Questar Gas acquisition of gas distribution system Payments to Acquire Businesses, Net of Cash Acquired Cash used in disposition of assets Payments for (Proceeds from) Removal Costs Proceeds from disposition of assets Proceeds from Sale of Productive Assets NET CASH USED IN INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Common stock issued Proceeds from Issuance of Common Stock Common stock repurchased Payments for Repurchase of Common Stock Change in short-term debt Proceeds from (Repayments of) Short-term Debt Change in notes receivable from Questar Increase (Decrease) in Notes Receivable, Related Parties Change in notes payable to Questar Increase (Decrease) in Notes Payable, Related Parties Checks outstanding in excess of cash balances Increase (Decrease) in Outstanding Checks, Financing Activities Long-term debt repaid Repayments of Long-term Debt Capital lease obligation repaid Repayments of Long-term Capital Lease Obligations Revolver issuance costs paid Payments of Debt Issuance Costs Dividends paid Payments of Dividends Dividends paid to Questar Payments of Distributions to Affiliates Tax benefits from share-based compensation Excess Tax Benefit from Share-based Compensation, Financing Activities NET CASH USED IN FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities Change in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Beginning cash and cash equivalents Ending cash and cash equivalents Number of principal complementary lines of business Business Acquisition, Date of Acquisition Agreement Business Acquisition, Date of Acquisition Agreement Business Acquisition, Share Price Business Acquisition, Share Price Maximum Extension to Merger Agreement MergerAgreementMaximumExtension Maximum extension rights as specified in the Merger Agreement. Business Acquisition, Acquirer Termination Fee Business Acquisition, Acquirer Termination Fee Termination fee receivable from the acquirer upon the termination of the Merger Agreement under specified circumstances. Business Acquisition, Acquiree Termination Fee Business Acquisition, Acquiree Termination Fee Termination fee payable by the acquiree upon the termination of the Merger Agreement under specified circumstances. Alternative Transaction Period AlternativeTransactionPeriod The Company will be required to pay Parent a termination fee in the event the Company signs an alternative transaction within twelve months following the termination of the Merger Agreement under certain specified circumstances. Business Acquisition Acquiree Reimbursement Fee BusinessAcquisitionAcquireeReimbursementFee Termination reimbursement fee receivable from the acquiree upon the termination of the Merger Agreement under specified circumstances. Loss Contingencies [Table] Loss Contingencies [Table] Unaffiliated Entity [Member] Unaffiliated Entity [Member] Unaffiliated Entity [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event [Member] Subsequent Event [Member] Litigation Status [Axis] Litigation Status [Axis] Litigation Status [Domain] Litigation Status [Domain] Pending Litigation [Member] Pending Litigation [Member] Pending Litigation, Third District Court, Salt Lake County, Utah [Member] Pending Litigation, Third District Court, Salt Lake County, Utah [Member] Pending Litigation, Third District Court, Salt Lake County, Utah [Member] Pending Litigation, United States District Court of Utah, Central Division [Member] Pending Litigation, United States District Court of Utah, Central Division [Member] Pending Litigation, United States District Court of Utah, Central Division [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Overriding royalty interest Overriding royalty interest Overriding royalty interest stipulated in original oil & gas lease assigned to Wexpro and QEP Energy Company. Loss Contingency, Range of Possible Loss, Maximum Loss Contingency, Range of Possible Loss, Maximum Loss Contingency, Pending Claims, Number Loss Contingency, Pending Claims, Number Fair Value Measurements Fair Value Disclosures [Text Block] Summary of operations by line of business Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Weighted Average Number of Shares Schedule of Weighted Average Number of Shares [Table Text Block]