Basis of Presentation of Interim Financial Statements (Policies)	3 Months Ended
Mar. 31, 2012
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature Of Business	Questar Corporation (Questar or the Company) is a Rockies-based integrated natural gas company with three complementary and wholly-owned lines of business: - Questar Gas Company (Questar Gas) provides retail natural gas distribution in Utah, Wyoming and Idaho. - Wexpro Company (Wexpro) develops and produces natural gas from cost-of-service reserves for Questar Gas. - Questar Pipeline Company (Questar Pipeline) operates interstate natural gas pipelines and storage facilities in the western United States and provides other energy services. Questar is headquartered in Salt Lake City, Utah. Shares of Questar common stock trade on the New York Stock Exchange (NYSE:STR).
Comprehensive Income - Questar	Comprehensive income attributable to Questar, as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income attributable to Questar as reported in the Consolidated Statements of Income and other comprehensive income (loss) (OCI). OCI includes recognition of the under-funded position of pension and other postretirement benefit plans, changes in the fair value of long-term investment, interest rate cash flow hedges and commodity-based derivative instruments, and income taxes. These transactions are not the culmination of the earnings process but result from periodically adjusting historical balances to fair value. Income or loss is recognized when the pension or other postretirement benefit costs are accrued, when the long-term investment is sold or otherwise realized, as the Company records interest expense for hedged interest payments and when gas, oil or NGL underlying the derivative instrument is sold.
Comprehensive Income - Questar Pipeline	Comprehensive income, as reported in Questar Pipeline's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Pipeline Consolidated Statements of Income and OCI. OCI includes interest rate cash flow hedges and income taxes. These transactions are not the culmination of the earnings process but result from periodically adjusting historical balances to fair value. Income or loss is recognized as the company records interest expense for hedged interest payments.
Investment in Unconsolidated Affiliate	Questar uses the equity method to account for its investment in an unconsolidated affiliate where it does not have control, but has significant influence. White River Hub, LLC is a limited liability company and FERC-regulated transporter of natural gas. Questar Pipeline owns 50% of White River Hub, LLC and is the operator. Generally, the investment in White River Hub, LLC on the Company's balance sheets equals the Company's proportionate share of equity reported by White River Hub, LLC. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below the Company's carrying value. When such a condition is deemed to be other than temporary, the carrying value of the investment is written down to its fair value, and the amount of the write-down is included in the determination of net income.
Earnings Per Share	Basic earnings per share (EPS) is computed by dividing net income attributable to Questar by the weighted-average number of common shares outstanding during the reporting period. Diluted EPS includes the potential increase in the number of outstanding shares that could result from the exercise of in-the-money stock options, the vesting of restricted stock units and performance shares that are part of the Company's Long-Term Stock Incentive Plan (LTSIP), less shares repurchased under the treasury stock method. Restricted stock units are participating securities for the computation of earnings per share. The application of the two-class method had an insignificant impact on the calculation of both basic and diluted EPS.
Asset Retirement Obligations	Questar records an asset retirement obligation (ARO) when there is a legal obligation associated with the retirement of a tangible long-lived asset. At Questar, AROs apply primarily to abandonment costs associated with gas and oil wells, production facilities and certain other properties. The Company has not capitalized future abandonment costs on a majority of its long-lived transportation and distribution assets because the Company does not have a legal obligation to restore the area surrounding abandoned assets. The fair value of retirement costs is estimated by Company personnel based on abandonment costs of similar properties available to field operations and depreciated over the life of the related assets. Revisions to ARO estimates result from changes in expected cash flows or material changes in estimated retirement costs. Income or expense resulting from the settlement of ARO liabilities is included in net gain (loss) from asset sales on the Consolidated Statements of Income. The ARO liability is adjusted to present value each period through an accretion calculation using a credit-adjusted risk-free interest rate.
Derivatives, Policy [Policy Text Block]	All derivative instruments are required to be recorded on the balance sheet as either assets or liabilities measured at fair value. The designation of a derivative instrument as a hedge and its ability to meet hedge accounting criteria determines how the changes in fair value of the derivative instrument are reflected in the consolidated financial statements. A derivative instrument qualifies for fair value hedge accounting if, at inception and throughout its life, the derivative is expected to be highly effective in offsetting the changes in fair value of the hedged debt attributable to the hedged interest rate. Changes in the fair value of a derivative instrument qualifying and designated as a fair value hedge as well as the offsetting changes in the fair value of the hedged debt attributable to the hedged interest rate are recorded currently in the Consolidated Statements of Income. A derivative instrument qualifies for cash flow hedge accounting if, at inception and throughout its life, the derivative is expected to be highly effective in offsetting the changes in expected cash flows of the hedged interest payments. Changes in the effective portion of the fair value of a derivative instrument qualifying and designated as a cash flow hedge are initially recorded as a component of OCI in the period and remain in AOCI in the Consolidated Balance Sheets until they are reclassified into earnings as the Company records interest expense for the hedged interest payments. Ineffective portions of a qualifying and designated cash flow hedge are recorded currently in earnings. All derivative instruments are recorded in the Consolidated Balance Sheets at their fair values on a gross basis. Asset and liability derivative positions with the same counterparty are not netted. Interest rate swaps and forward starting interest rate swaps are settled in cash on periodic payment dates with one party paying the other for the net difference between the fixed and floating interest rate for the payment period as specified in the swap agreement, multiplied by the notional amount. Forward starting interest rate swaps used as cash flow hedges of forecasted fixed-rate debt issuances are terminated and settled in cash when the forecasted debt is issued or as the swaps expire, with one party paying the other for the swap's net fair value at the time of settlement. Questar reports cash flows related to derivative instruments qualifying and designated as hedges in the Consolidated Statements of Cash Flows based upon the nature of the hedged items.
Business Segments	Line-of-business information is presented according to senior management's basis for evaluating performance and considering differences in the nature of products, services and regulation, among other factors.

Basis of Presentation of Interim Financial Statements (Policies)

3 Months Ended

Mar. 31, 2012

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Questar Corporation (Questar or the Company) is a Rockies-based integrated natural gas company with three complementary and wholly-owned lines of business:

- Questar Gas Company (Questar Gas) provides retail natural gas distribution in Utah, Wyoming and Idaho.

- Wexpro Company (Wexpro) develops and produces natural gas from cost-of-service reserves for Questar Gas.

- Questar Pipeline Company (Questar Pipeline) operates interstate natural gas pipelines and storage facilities in the western

United States and provides other energy services.

Questar is headquartered in Salt Lake City, Utah. Shares of Questar common stock trade on the New York Stock Exchange (NYSE:STR).

Comprehensive Income - Questar

Comprehensive income attributable to Questar, as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income attributable to Questar as reported in the Consolidated Statements of Income and other comprehensive income (loss) (OCI). OCI includes recognition of the under-funded position of pension and other postretirement benefit plans, changes in the fair value of long-term investment, interest rate cash flow hedges and commodity-based derivative instruments, and income taxes. These transactions are not the culmination of the earnings process but result from periodically adjusting historical balances to fair value. Income or loss is recognized when the pension or other postretirement benefit costs are accrued, when the long-term investment is sold or otherwise realized, as the Company records interest expense for hedged interest payments and when gas, oil or NGL underlying the derivative instrument is sold.

Comprehensive Income - Questar Pipeline

Comprehensive income, as reported in Questar Pipeline's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Pipeline Consolidated Statements of Income and OCI. OCI includes interest rate cash flow hedges and income taxes. These transactions are not the culmination of the earnings process but result from periodically adjusting historical balances to fair value. Income or loss is recognized as the company records interest expense for hedged interest payments.

Investment in Unconsolidated Affiliate

Questar uses the equity method to account for its investment in an unconsolidated affiliate where it does not have control, but has significant influence. White River Hub, LLC is a limited liability company and FERC-regulated transporter of natural gas. Questar Pipeline owns 50% of White River Hub, LLC and is the operator. Generally, the investment in White River Hub, LLC on the Company's balance sheets equals the Company's proportionate share of equity reported by White River Hub, LLC. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below the Company's carrying value. When such a condition is deemed to be other than temporary, the carrying value of the investment is written down to its fair value, and the amount of the write-down is included in the determination of net income.

Earnings Per Share

Basic earnings per share (EPS) is computed by dividing net income attributable to Questar by the weighted-average number of common shares outstanding during the reporting period. Diluted EPS includes the potential increase in the number of outstanding shares that could result from the exercise of in-the-money stock options, the vesting of restricted stock units and performance shares that are part of the Company's Long-Term Stock Incentive Plan (LTSIP), less shares repurchased under the treasury stock method. Restricted stock units are participating securities for the computation of earnings per share. The application of the two-class method had an insignificant impact on the calculation of both basic and diluted EPS.

Asset Retirement Obligations

Questar records an asset retirement obligation (ARO) when there is a legal obligation associated with the retirement of a tangible long-lived asset. At Questar, AROs apply primarily to abandonment costs associated with gas and oil wells, production facilities and certain other properties. The Company has not capitalized future abandonment costs on a majority of its long-lived transportation and distribution assets because the Company does not have a legal obligation to restore the area surrounding abandoned assets. The fair value of retirement costs is estimated by Company personnel based on abandonment costs of similar properties available to field operations and depreciated over the life of the related assets. Revisions to ARO estimates result from changes in expected cash flows or material changes in estimated retirement costs. Income or expense resulting from the settlement of ARO liabilities is included in net gain (loss) from asset sales on the Consolidated Statements of Income. The ARO liability is adjusted to present value each period through an accretion calculation using a credit-adjusted risk-free interest rate.

Derivatives, Policy [Policy Text Block]

All derivative instruments are required to be recorded on the balance sheet as either assets or liabilities measured at fair value. The designation of a derivative instrument as a hedge and its ability to meet hedge accounting criteria determines how the changes in fair value of the derivative instrument are reflected in the consolidated financial statements. A derivative instrument qualifies for fair value hedge accounting if, at inception and throughout its life, the derivative is expected to be highly effective in offsetting the changes in fair value of the hedged debt attributable to the hedged interest rate. Changes in the fair value of a derivative instrument qualifying and designated as a fair value hedge as well as the offsetting changes in the fair value of the hedged debt attributable to the hedged interest rate are recorded currently in the Consolidated Statements of Income. A derivative instrument qualifies for cash flow hedge accounting if, at inception and throughout its life, the derivative is expected to be highly effective in offsetting the changes in expected cash flows of the hedged interest payments. Changes in the effective portion of the fair value of a derivative instrument qualifying and designated as a cash flow hedge are initially recorded as a component of OCI in the period and remain in AOCI in the Consolidated Balance Sheets until they are reclassified into earnings as the Company records interest expense for the hedged interest payments. Ineffective portions of a qualifying and designated cash flow hedge are recorded currently in earnings.

All derivative instruments are recorded in the Consolidated Balance Sheets at their fair values on a gross basis. Asset and liability derivative positions with the same counterparty are not netted.

Interest rate swaps and forward starting interest rate swaps are settled in cash on periodic payment dates with one party paying the other for the net difference between the fixed and floating interest rate for the payment period as specified in the swap agreement, multiplied by the notional amount. Forward starting interest rate swaps used as cash flow hedges of forecasted fixed-rate debt issuances are terminated and settled in cash when the forecasted debt is issued or as the swaps expire, with one party paying the other for the swap's net fair value at the time of settlement. Questar reports cash flows related to derivative instruments qualifying and designated as hedges in the Consolidated Statements of Cash Flows based upon the nature of the hedged items.

Business Segments

Line-of-business information is presented according to senior management's basis for evaluating performance and considering differences in the nature of products, services and regulation, among other factors.

- Definition

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.

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- Definition

Disclosure of accounting policy for its derivative instruments and hedging activities. Disclosure may include: (1) Each method used to account for derivative financial instruments and derivative commodity instruments ("derivatives"); (2) the types of derivatives accounted for under each method; (3) the criteria required to be met for each accounting method used, including a discussion of the criteria required to be met for hedge or deferral accounting and accrual or settlement accounting (for example, whether and how risk reduction, correlation, designation, and effectiveness tests are applied); (4) the accounting method used if the criteria specified for hedge accounting are not met; (5) the method used to account for termination of derivatives designated as hedges or derivatives used to affect directly or indirectly the terms, fair values, or cash flows of a designated item; (6) the method used to account for derivatives when the designated item matures, is sold, is extinguished, or is terminated. In addition, the method used to account for derivatives designated to an anticipated transaction, when the anticipated transaction is no longer likely to occur; and (7) where and when derivatives, and their related gains or losses are reported in the statement of financial position, cash flows, and results of operations and (8) an accounting policy decision to offset fair value amounts with counterparties. An entity may also describe its embedded derivatives, and the method(s) used to determine the fair values of derivatives and any significant assumptions used in such valuations.

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Disclosure of accounting policy for computing basic and diluted earnings or loss per share for each class of common stock and participating security. Addresses all significant policy factors, including any antidilutive items that have been excluded from the computation and takes into account stock dividends, splits and reverse splits that occur after the balance sheet date of the latest reporting period but before the issuance of the financial statements.

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- Definition

Disclosure of accounting policy for the equity method of accounting for investments in common stock or other interests including unconsolidated subsidiaries, corporate joint ventures, noncontrolling interests in real estate ventures, limited partnerships, and limited liability companies. The accounting policy may include information such as: (1) initially recording an investment in the stock of an investee at cost; (2) adjusting the carrying amount of the investment to recognize the investor's share of the earnings or losses of the investee after the date of acquisition; and (3) adjustments to reflect the investor's share of changes in the investee's capital (dividends). This disclosure may also include a detailed description of the policy for determining the amount of equity method losses recognized after an investment has been reduced to zero as a result of previous losses, reasons for not using the equity method when the investor company owns 20 percent or more of the voting stock of the investee's company (including identification of the significant investee), reasons for using the equity method when the ownership percentage is less than 20 percent, and discussion of recognition of equity method losses when an investor's total investment in an investee includes, in addition to an investment in common stock, other investments such as preferred stock and loans to the investee. An entity also may describe how such investments are assessed for impairment.

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