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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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

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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 35
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=56949341&loc=d3e75592-113984

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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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Debt Long-term Debt (Details) - USD ($) $ in Millions	12 Months Ended
Debt Long-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Total long-term debt outstanding	$ 1,219.5	$ 1,244.6
Less current portion	(250.2)	(25.1)
Less unamortized debt discount	(1.7)	(1.9)
Plus unamortized debt premium	0.3	0.5
Plus fair value hedge adjustment	0.2	2.0
Total long-term debt, less current portion	$ 968.1	1,220.1
Questar Corp [Member] \| 2.75% Notes due 2016 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 250.0
Debt Instrument, Interest Rate, Stated Percentage	2.75%		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	534.5
Total long-term debt, less current portion	$ 534.5	534.5
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%
Debt Instrument, Maturity Date	Dec. 01, 2024
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%
Debt Instrument, Maturity Date	Dec. 01, 2027
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
Total long-term debt outstanding	$ 90.0	90.0
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
Total long-term debt outstanding	$ 60.0	60.0
Questar Pipeline [Member]
Debt Instrument [Line Items]
Total long-term debt outstanding	435.0	460.1
Total long-term debt, less current portion	$ 433.6	433.7
Questar Pipeline [Member] \| 6.48% Medium-term Notes due 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	$ 5.0	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