Summary of Significant Accounting Policies (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2010	Dec. 31, 2011 bbl Mcfe lines_of_business	Dec. 31, 2010	Dec. 31, 2009
Nature of Business [Abstract]
Number Of Business Lines		3
Principles of Consolidation [Abstract]
Approval date of Reincorporation Merger		5/18/2010
Distribution date of tax-free, pro rata dividend to Questar shareholders		6/30/2010
Number of shares of QEP common stock received for each share of Questar common stock		1
Equity contribution to QEP prior to Spinoff	$ 250,000,000	$ 0	$ 250,000,000	$ 0
Separation costs		0	11,500,000	0
Revenue Recognition [Abstract]
After tax rate of return allowed per Wexpro agreement (In hundredths)		20.00%
Percentage of operating income retained by Wexpro after expenses (in hundredths)		46.00%
Cash and Cash Equivalents [Abstract]
Cash Equivalent Maturity Maximum Months		3 months
Depreciation, depletion and amortization [Abstract]
Crude Oil To Be Converted To Natural Gas		1
Oil Conversion To Natural Gas Cubic Feet		6,000
Cost-of-service gas and oil properties, per Mcfe		1.49	1.47	1.44
Questar Pipeline transportation, storage and other energy services		3.50%	3.50%	3.50%
Questar Gas distribution plant		2.80%	2.90%	3.00%
Gas Distribution Plant Reduction In Annual Depreciation Expense		3,600,000
Impairment of long-lived assets [Abstract]
Total impairment expense		0	0	0
Capitalized Interest and funds used for construction [Abstract]
AFUDC (recorded as an increase in interest and other income)		4,400,000	2,700,000	2,600,000
Capitalized interest costs (recorded as a reduction of interest expense)		600,000	1,200,000	1,200,000
Credit Risk [Abstract]
Provision for Doubtful Accounts		2,400,000	500,000	3,400,000
Reduction in bad-debt expense from the settlement of a revenue dispute previously accrued for in allowance for bad debts			1,500,000
Allowance for Doubtful Accounts Receivable		3,200,000	3,200,000
Income Taxes [Abstract]
Unrecognized tax benefits		0	0	0
Percent of capital expenditures deductible for federal income tax purposes under current statutes (in hundredths)		100.00%
Net operating loss (NOL) for federal income tax purposes			102,000,000
Expiration date of net operating loss (NOL) for federal income tax purposes		2031
Accumulated other comprehensive loss [Abstract]
Pension liability		(182,700,000)	(93,200,000)
Postretirement benefits liability		(20,100,000)	(10,900,000)
Interest rate cash flow hedges		(23,400,000)	0
Long-term investment		100,000	100,000
Accumulated other comprehensive loss		(226,100,000)	(104,000,000)
Income taxes allocated to each component of other comprehensive income (loss) [Abstract]
Pension liability		55,500,000	(7,000,000)	(15,500,000)
Postretirement benefits liability		5,700,000	(1,200,000)	(2,800,000)
Interest rate cash flow hedges		13,800,000	0	0
Discontinued operations, unrealized gain (loss) on derivatives		0	51,600,000	150,600,000
Income Taxes		75,000,000	43,400,000	132,300,000
Derivatives used in cash flow hedge, AOCI, net of tax [Roll Forward]
Interest rate cash flow hedges beginning balance		0
Interest rate cash flow hedges ending balance		(23,400,000)	0
Wexpro [Member]
Capitalized Interest and funds used for construction [Abstract]
AFUDC (recorded as an increase in interest and other income)		3,300,000	2,400,000	1,900,000
Questar Pipeline [Member]
Principles of Consolidation [Abstract]
Ownership percentage in unconsolidated affiliate (in hundredths)		50.00%
Capitalized Interest and funds used for construction [Abstract]
AFUDC (recorded as an increase in interest and other income)		1,100,000	300,000	700,000
Capitalized interest costs (recorded as a reduction of interest expense)		500,000	1,000,000	900,000
Accumulated other comprehensive loss [Abstract]
Interest rate cash flow hedges		(23,400,000)	0	0
Accumulated other comprehensive loss		(23,400,000)	0
Income taxes allocated to each component of other comprehensive income (loss) [Abstract]
Income Taxes		13,800,000
Derivatives used in cash flow hedge, AOCI, net of tax [Roll Forward]
Interest rate cash flow hedges beginning balance	0	0	0
Net change associated with current period hedging transactions		(23,500,000)	0
Net amount reclassified into earnings		100,000	0
Interest rate cash flow hedges ending balance		(23,400,000)	0	0
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%
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
Capitalized Interest and funds used for construction [Abstract]
Capitalized interest costs (recorded as a reduction of interest expense)		$ 100,000	$ 200,000	$ 300,000
Credit Risk [Abstract]
Time period in months uncollected accounts are written off		6 months