Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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Interest payment due to decline in fixed interest rate on fixed-rate debt.

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Life of Long-Term Debt Associated with Cash Flow Hedges (in years)

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The time period estimated for the anticipated transfer of gains (losses), net from accumulated other comprehensive income into earnings.

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994

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- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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-Publisher FASB

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-SubTopic 30

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-Name Accounting Principles Board Opinion (APB)

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Average fixed interest rate related to the group of interest rate derivatives.

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- Definition

Increase in the fair value of the derivative or group of derivatives included in earnings in the period.

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The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

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Net gain (loss) recognized in earnings during the reporting period representing the amount of the fair value of the hedges' ineffectiveness.

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-Name Statement of Financial Accounting Standard (FAS)

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Disclosure of an assertion that the amount of interest rate cash flow hedge ineffectiveness is immaterial.

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Derivative Instruments and Hedging Activities Additional Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended			1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2013 Cash Flow Hedging [Member] Questar Pipeline [Member] Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]	Mar. 31, 2012 Cash Flow Hedging [Member] Questar Pipeline [Member] Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]	Mar. 31, 2013 Cash Flow Hedging [Member] Questar Pipeline [Member] Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]	Mar. 31, 2012 Cash Flow Hedging [Member] Questar Pipeline [Member] Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]	Dec. 31, 2011 Cash Flow Hedging [Member] Questar Pipeline [Member] Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]	Mar. 31, 2012 Fair Value Hedging [Member] Interest Rate Swap [Member]	Mar. 31, 2013 Fair Value Hedging [Member] Interest Rate Swap [Member]	Mar. 31, 2012 Fair Value Hedging [Member] Interest Rate Swap [Member]	Mar. 31, 2013 Fair Value Hedging [Member] Interest Rate Swap [Member]	Mar. 31, 2012 Fair Value Hedging [Member] Interest Rate Swap [Member]	Jun. 30, 2011 Fair Value Hedging [Member] Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount					$ 150.0						$ 125.0
Weighted-average fixed interest rate (in hundredths)											2.75%
Derivative, gain on derivative						7.2
Debt instrument, face amount					180.0
Interest payment for terminated derivative instrument					37.3
Life of long-term debt associated with cash flow hedges					30 years
Ineffectiveness recognized on the fair value hedge							0	0	0	0
Ineffectiveness recognized on cash flow hedges	0	0	0
Interest Rate Cash Flow Hedge Ineffectiveness is Immaterial				Ineffectiveness recognized on the cash flow hedges was de minimis
Pre-tax net losses expected to be reclassified from AOCI to Consolidated statement of income	$ 0.5
Reclassification from accumulated OCI to income, estimated time to transfer	12 months