Debt Long-term Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Total long-term debt outstanding	$ 1,244.6	$ 1,136.6
Less current portion	0	(42.0)
Less unamortized-debt discount	(2.1)	(2.3)
Plus unamortized-debt premium	0.7	0.8
Plus fair value hedge adjustment	3.9	5.8
Total long-term debt, less current portion	1,247.1	1,098.9
Questar Corp [Member] \| 2.75% Notes due 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.75%
Debt Instrument, Maturity Date	Feb. 01, 2016
Total long-term debt outstanding	250.0	250.0
Questar Gas [Member]
Debt Instrument [Line Items]
Total long-term debt outstanding	534.5	426.5
Total long-term debt, less current portion	534.5	384.5
Questar Gas [Member] \| 5.00% and 6.89% Medium-term Notes due 2013 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	5.00%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	6.89%
Debt Instrument, Maturity Date	Jan. 24, 2013
Total long-term debt outstanding	0	42.0
Questar Gas [Member] \| 5.31% and 6.85% Medium-term Notes due 2017 and 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	5.31%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	6.85%
Debt Instrument, Maturity Date Range, Start	Oct. 10, 2017
Debt Instrument, Maturity Date Range, End	Mar. 15, 2018
Total long-term debt outstanding	84.5	84.5
Questar Gas [Member] \| 6.30% Notes due 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.30%
Debt Instrument, Maturity Date	Apr. 01, 2018
Total long-term debt outstanding	50.0	50.0
Questar Gas [Member] \| 2.98% Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.98%	2.98%
Debt Instrument, Maturity Date	Dec. 01, 2024
Debt instrument, face amount		40.0
Debt Instrument, Term		12 years
Total long-term debt outstanding	40.0	40.0
Questar Gas [Member] \| 3.28% Notes due 2027 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.28%	3.28%
Debt Instrument, Maturity Date	Dec. 01, 2027
Debt instrument, face amount		110.0
Debt Instrument, Term		15 years
Total long-term debt outstanding	110.0	110.0
Questar Gas [Member] \| 7.20% Notes due 2038 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.20%
Debt Instrument, Maturity Date	Apr. 01, 2038
Total long-term debt outstanding	100.0	100.0
Questar Gas [Member] \| 4.78% Notes due 2043 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.78%
Debt Instrument, Maturity Date	Dec. 01, 2043
Debt instrument, face amount	90.0
Debt Instrument, Term	30 years
Total long-term debt outstanding	90.0	0
Questar Gas [Member] \| 4.83% Notes due 2048 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.83%
Debt Instrument, Maturity Date	Dec. 01, 2048
Debt instrument, face amount	60.0
Debt Instrument, Term	35 years
Total long-term debt outstanding	60.0	0
Questar Gas [Member] \| Questar Gas Notes due 2012 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date		Oct. 01, 2012
Long-Term Debt Amounts Repaid During the Year		91.5
Questar Gas [Member] \| Questar Gas Notes Due January 2013 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date		Jan. 24, 2013
Long-Term Debt Amounts Repaid During the Year		40.0
Questar Gas [Member] \| Questar Gas Notes due September 2013 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date		Sep. 30, 2013
Long-Term Debt Amounts Repaid During the Year		2.0
Questar Gas [Member] \| Questar Gas Notes refinanced in December 2012 [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate		6.06%
Questar Gas [Member] \| 2.98% and 3.28% Notes due 2024 and 2027 [Member]
Debt Instrument [Line Items]
Net Proceeds from Issuance of Long-Term Debt		148.8
Questar Gas [Member] \| 4.78% and 4.83% Notes due 2043 and 2048 [Member]
Debt Instrument [Line Items]
Net Proceeds from Issuance of Long-Term Debt	149.0
Questar Pipeline [Member]
Debt Instrument [Line Items]
Total long-term debt outstanding	460.1	460.1
Total long-term debt, less current portion	458.9	458.9
Questar Pipeline [Member] \| 6.45% and 6.48% Medium-term Notes due 2015 and 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	6.45%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	6.48%
Debt Instrument, Maturity Date Range, Start	Oct. 15, 2015
Debt Instrument, Maturity Date Range, End	Dec. 11, 2018
Total long-term debt outstanding	30.1	30.1
Questar Pipeline [Member] \| 5.83% Notes due 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.83%
Debt Instrument, Maturity Date	Feb. 01, 2018
Total long-term debt outstanding	250.0	250.0
Questar Pipeline [Member] \| 4.875% Notes due 2041 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Debt Instrument, Maturity Date	Dec. 01, 2041
Total long-term debt outstanding	$ 180.0	$ 180.0

Long-Term Debt Amounts Repaid During the Year

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Net Proceeds from Issuance of Long-Term Debt

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Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Maximum contractual interest rate for funds borrowed, under the debt agreement.

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Minimum contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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The amount of debt premium that was originally recognized at the issuance of the instrument that has yet to be amortized.

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Weighted average interest rate of debt outstanding.

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No definition available.

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- Definition

Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective fair value hedge that is amortized upon discontinuation of the fair value hedge.

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Sum of the carrying values as of the balance sheet date of the portions of long-term notes payable due within one year or the operating cycle if longer.

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