Summary of Significant Accounting Policies (Details)	3 Months Ended						12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)	Dec. 31, 2015 USD ($) lines_of_business bbl	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Nature of Business [Abstract]
Number Of Business Lines | lines_of_business							3
Revenue Recognition [Abstract]
Percentage of operating income retained by Wexpro after expenses (in hundredths)	46.00%						46.00%
Cost of Sales [Abstract]
Other cost of sales							$ 1,700,000	$ 900,000	$ 100,000
Total cost of sales							175,200,000	186,300,000	285,900,000
Derivative Assets (Liabilities), at Fair Value, Net	$ 200,000						$ 200,000	0
Cash and Cash Equivalents [Abstract]
Cash equivalent maturity maximum (months)							3 months
Depreciation, depletion and amortization [Abstract]
Barrel of oil conversion to 6,000 cubic feet of natural gas | bbl							1
Impairment of Long-Lived Assets [Abstract]
Abandonment and impairment							$ 12,500,000	2,000,000	80,600,000
Capitalized Interest and Allowance for Funds Used During Construction [Abstract]
AFUDC (recorded as an increase in interest and other income)							1,200,000	2,800,000	6,300,000
Capitalized interest costs (recorded as a reduction of interest expense)							300,000	1,000,000	800,000
Credit Risk [Abstract]
Bad debt expense							2,100,000	1,700,000	200,000
Allowance for bad debts	2,100,000						2,100,000	1,700,000
Income Taxes [Abstract]
Unrecognized tax benefits	$ 0						$ 0	$ 0	$ 0
Percent of capital expenditures deductible for federal income tax purposes under current statutes (in hundredths)								50.00%	50.00%
Questar Gas [Member]
Revenue Recognition [Abstract]
Rate Adjustment Time Period							6 months
Deferred CET adjustments amortization period							12 months
Rate adjustment limitation as a percent of non-gas revenues (In hundredths)	5.00%						5.00%
Cost of Sales [Abstract]
Gas purchases							$ 82,500,000	$ 136,500,000	$ 186,600,000
Operator service fee							319,000,000	349,700,000	294,600,000
Transportation and storage							79,200,000	79,600,000	80,100,000
Gathering							22,100,000	21,000,000	18,800,000
Royalties							33,300,000	60,100,000	44,300,000
Storage (injection),net							(3,500,000)	(1,100,000)	(800,000)
Purchased-gas account adjustment							20,500,000	(45,800,000)	22,000,000
Other							5,000,000	4,800,000	5,000,000
Total cost of natural gas sold (excluding operating expenses shown separately) / Total Questar Gas cost of natural gas sold							558,100,000	604,800,000	650,600,000
Elimination of Questar Gas cost of natural gas sold - affiliated companies							(393,500,000)	(423,400,000)	(370,900,000)
Total Questar Gas cost of natural gas sold - unaffiliated parties							$ 164,600,000	$ 181,400,000	$ 279,700,000
Contributions in aid of construction [Abstract]
Time period contributions are refundable if other customers pay to connect to the line (in years)							5 years
Time period if no other customers connect to the line the funds are not refundable (in years)							5 years
Depreciation, depletion and amortization [Abstract]
Questar Gas distribution plant							2.60%	2.70%	2.70%
Capitalized Interest and Allowance for Funds Used During Construction [Abstract]
AFUDC (recorded as an increase in interest and other income)							$ 0	$ 900,000	$ 0
Capitalized interest costs (recorded as a reduction of interest expense)							$ 100,000	500,000	200,000
Credit Risk [Abstract]
Time period in months uncollected accounts are written off							6 months
Wexpro [Member]
Depreciation, depletion and amortization [Abstract]
Cost-of-service gas and oil properties, per Mcfe							$ 1.83	1.75	1.56
Impairment of Long-Lived Assets [Abstract]
Abandonment and impairment	$ 12,100,000	$ 0	$ 0	$ 0			12,100,000
Capitalized Interest and Allowance for Funds Used During Construction [Abstract]
AFUDC (recorded as an increase in interest and other income)							$ 600,000	800,000	4,600,000
Wexpro Brady Field [Member]
Impairment of Long-Lived Assets [Abstract]
Abandonment and impairment					$ 2,000,000
Questar Pipeline [Member]
Investment in Unconsolidated Affiliate [Abstract]
Ownership percentage in unconsolidated affiliate (in hundredths)	50.00%						50.00%
Cost of Sales [Abstract]
Total Questar Pipeline cost of sales							$ 8,900,000	$ 4,000,000	$ 6,100,000
Depreciation, depletion and amortization [Abstract]
Questar Pipeline transportation, storage and other energy services							3.20%	3.20%	3.40%
Impairment of Long-Lived Assets [Abstract]
Abandonment and impairment						$ 80,600,000	$ 0	$ 0	$ 80,600,000
Capitalized Interest and Allowance for Funds Used During Construction [Abstract]
AFUDC (recorded as an increase in interest and other income)							600,000	1,100,000	1,700,000
Capitalized interest costs (recorded as a reduction of interest expense)							200,000	$ 500,000	$ 600,000
Income Taxes [Abstract]
Property, Plant, and Equipment, Fair Value Disclosure	$ 24,000,000						$ 24,000,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Wexpro [Member]
Income Taxes [Abstract]
Property, Plant, and Equipment, Fair Value Disclosure					$ 0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Questar Pipeline [Member]
Income Taxes [Abstract]
Property, Plant, and Equipment, Fair Value Disclosure						$ 0