Dominion Questar 10-Q 30 Apr 15 2015 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2015
Entity Information [Line Items]
Entity Registrant Name	QUESTAR CORP
Entity Central Index Key	751652
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding	175,712,882
Questar Gas [Member]
Entity Information [Line Items]
Entity Registrant Name	QUESTAR GAS CO
Entity Central Index Key	68589
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding	9,189,626
Questar Pipeline [Member]
Entity Information [Line Items]
Entity Registrant Name	QUESTAR PIPELINE CO
Entity Central Index Key	764044
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding	6,550,843

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	3 Months Ended		12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
REVENUES
Questar Gas / Revenues from unaffiliated customers	$374.80	$396.30	$939.40	$963.20
Wexpro	6.3	12.3	29.6	47.1
Questar Pipeline / Revenues from unaffiliated customers	46.8	48	189	189.2
Other	0.7	0.3	3	0.5
Total Revenues	428.6	456.9	1,161	1,200
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	131.8	148.2	169.9	234.4
Operating and maintenance	52.3	56.9	189.6	186.7
General and administrative	29.4	30.3	121.8	113.8
Production and other taxes	13.8	17.9	62.1	60
Depreciation, depletion and amortization	54.3	55.3	212.7	201.6
Abandonment and impairment	0	0	2	80.6
Total Operating Expenses	281.6	308.6	758.1	877.1
Net gain (loss) from asset sales	0	0	1.2	-0.2
OPERATING INCOME	147	148.3	404.1	322.7
Interest and other income	1.4	1.8	6.2	8.7
Income from unconsolidated affiliate	0.9	0.9	3.5	3.7
Interest expense	-15.9	-15.8	-63.2	-58.2
INCOME BEFORE INCOME TAXES	133.4	135.2	350.6	276.9
Income taxes	-48.8	-50.1	-124.6	-103.5
NET INCOME	84.6	85.1	226	173.4
Earnings Per Common Share
Basic	$0.48	$0.48	$1.29	$0.98
Diluted	$0.48	$0.48	$1.28	$0.98
Weighted-average common shares outstanding
Used in basic calculation	176.2	175.7	176	175.6
Used in diluted calculation	176.5	176.1	176.3	176.1
Dividends per common share	$0.21	$0.18	$0.78	$0.72
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	374.8	396.3	939.4	963.2
Revenues from affiliated company	0	0	0	0.3
Total Revenues	374.8	396.3	939.4	963.5
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	233.6	254.6	583.8	614.6
Operating and maintenance	33.1	39.8	115.8	119.2
General and administrative	13.4	13.8	52.4	53.6
Depreciation and amortization	13.5	13.2	53.9	50.8
Other taxes	4.6	5.1	17.3	17.9
Total Operating Expenses	298.2	326.5	823.2	856.1
Net gain (loss) from asset sales	0	0	0.1	0
OPERATING INCOME	76.6	69.8	116.3	107.4
Interest and other income	1.1	1.3	5.7	5.2
Interest expense	-7.1	-7.1	-28.2	-23.6
INCOME BEFORE INCOME TAXES	70.6	64	93.8	89
Income taxes	-26.8	-24.4	-34.4	-33.6
NET INCOME	43.8	39.6	59.4	55.4
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	46.8	48	189	189.2
Revenues from affiliated companies	19.4	19.3	73.8	76.5
Total Revenues	66.2	67.3	262.8	265.7
OPERATING EXPENSES
Operating and maintenance	10.1	9.3	40.1	38.1
General and administrative	10.5	10.3	39.1	40.9
Depreciation and amortization	14	13.6	54.9	55
Abandonment and impairment	0	0	0	80.6
Other taxes	2.3	2.3	9.1	9.1
Cost of sales (excluding operating expenses shown separately)	1.9	1.7	4.2	6.6
Total Operating Expenses	38.8	37.2	147.4	230.3
Net gain (loss) from asset sales	0	0	-0.5	0
OPERATING INCOME	27.4	30.1	114.9	35.4
Interest and other income	0.2	0.3	1.1	1.8
Income from unconsolidated affiliate	0.9	0.9	3.5	3.7
Interest expense	-6.6	-6.5	-26.2	-25.8
INCOME BEFORE INCOME TAXES	21.9	24.8	93.3	15.1
Income taxes	-8	-9.1	-34.5	-7
NET INCOME	$13.90	$15.70	$58.80	$8.10

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Net income	$84.60	$85.10	$226	$173.40
Other comprehensive income (loss):
Pension and other postretirement benefits	6	4.3	-95.2	165.3
Interest rate cash flow hedge amortization	0.2	0.2	0.5	0.5
Change in fair value of long-term investment	0	0	0	-0.1
Income taxes	-2.4	-1.8	36.3	-63.5
Net other comprehensive income (loss)	3.8	2.7	-58.4	102.2
COMPREHENSIVE INCOME	88.4	87.8	167.6	275.6
Questar Pipeline [Member]
Net income	13.9	15.7	58.8	8.1
Other comprehensive income (loss):
Interest rate cash flow hedge amortization	0.2	0.2	0.5	0.5
Income taxes	-0.1	-0.1	-0.1	-0.2
Net other comprehensive income (loss)	0.1	0.1	0.4	0.3
COMPREHENSIVE INCOME	$14	$15.80	$59.20	$8.40

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Millions, unless otherwise specified
Current Assets
Cash and cash equivalents	$4.80	$32	$5.60
Accounts receivable, net	104.5	118.1	130.6
Unbilled gas accounts receivable	41.5	93.7	56.3
Gas stored underground	12.4	43.7	6.9
Materials and supplies	28.7	30.4	25
Current regulatory assets	43	79.6	29.8
Prepaid expenses and other	8.7	11.2	7.5
Deferred income taxes - current	8.2	5.8	14.5
Total Current Assets	251.8	414.5	276.2
Property, Plant and Equipment	6,033.10	5,961.50	5,723.50
Accumulated depreciation, depletion and amortization	-2,277.20	-2,226	-2,121.60
Net Property, Plant and Equipment	3,755.90	3,735.50	3,601.90
Investment in unconsolidated affiliate	24.5	24.7	25.2
Noncurrent regulatory assets	23.6	25	19.3
Other noncurrent assets	50.1	50	51.8
TOTAL ASSETS	4,105.90	4,249.70	3,974.40
Current Liabilities
Short-term debt	214	347	157
Accounts payable and accrued expenses	200.5	234.9	229.9
Current regulatory liabilities	5.2	13.4	17.2
Current portion of long-term debt and capital lease obligation	277.8	26.1	0.9
Total Current Liabilities	697.5	621.4	405
Long-term debt and capital lease obligation, less current portion	1,005.10	1,257.50	1,284.70
Deferred income taxes	716.6	715.6	712.6
Asset retirement obligations	75	69.3	68.6
Defined benefit pension plan and other postretirement benefits	155.7	185.7	108.5
Noncurrent regulatory liabilities	72.5	69.9	63.2
Customer contributions in aid of construction	28	29.2	32
Other noncurrent liabilities	57.2	54.9	43.6
COMMON SHAREHOLDERS' EQUITY
Common stock	477.6	476.8	465.7
Retained earnings	1,018.20	970.7	929.6
Accumulated other comprehensive (loss)	-197.5	-201.3	-139.1
Total Common Shareholders' Equity	1,298.30	1,246.20	1,256.20
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	4,105.90	4,249.70	3,974.40
Questar Gas [Member]
Current Assets
Cash and cash equivalents	0	19.8	1.4
Notes receivable from Questar	0	0	30.6
Accounts receivable, net	81.2	66.4	102.6
Unbilled gas accounts receivable	41.5	93.7	56.3
Accounts receivable from affiliates	56.3	45.2	31.3
Gas stored underground	9.5	40.3	6.2
Materials and supplies	17.3	19.2	13.2
Current regulatory assets	42.1	78.3	24
Prepaid expenses and other	2.4	3.5	2.4
Deferred income taxes - current	0	0	2.9
Total Current Assets	250.3	366.4	270.9
Property, Plant and Equipment	2,400.70	2,352.30	2,230
Accumulated depreciation, depletion and amortization	-791.5	-780.3	-754.3
Net Property, Plant and Equipment	1,609.20	1,572	1,475.70
Noncurrent regulatory assets	20.3	21.3	15.4
Other noncurrent assets	9.2	9.3	9.5
TOTAL ASSETS	1,889	1,969	1,771.50
Current Liabilities
Checks outstanding in excess of cash balances	0.4	0	0
Notes payable to Questar	35.8	119.3	0
Accounts payable and accrued expenses	126	111.9	111.3
Accounts payable to affiliates	71.4	78.7	65.6
Dividends payable to Questar	0	9	0
Customer advances	9.5	29.4	7.2
Current regulatory liabilities	4.3	12.5	15.2
Deferred income taxes - current	3.9	6.3	0
Total Current Liabilities	251.3	367.1	199.3
Long-term debt and capital lease obligation, less current portion	534.5	534.5	534.5
Deferred income taxes	377.5	377.5	340.6
Noncurrent regulatory liabilities	63.3	60.9	54.8
Customer contributions in aid of construction	28	29.2	32
Other noncurrent liabilities	2.8	2.8	3.1
COMMON SHAREHOLDERS' EQUITY
Common stock	23	23	23
Additional paid-in capital	265.7	265.4	264.2
Retained earnings	342.9	308.6	320
Total Common Shareholders' Equity	631.6	597	607.2
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	1,889	1,969	1,771.50
Questar Pipeline [Member]
Current Assets
Cash and cash equivalents	6.1	7.4	4.9
Notes receivable from Questar	35.9	40.1	46.6
Accounts receivable, net	16.8	17.9	17.5
Accounts receivable from affiliates	44.3	39.2	33.8
Gas stored underground	2.9	3.4	0.7
Materials and supplies	7.1	6.9	7.5
Current regulatory assets	0.9	1.3	5.8
Prepaid expenses and other	3.6	4.3	2.8
Deferred income taxes - current	1.9	1.9	1.8
Total Current Assets	119.5	122.4	121.4
Property, Plant and Equipment	1,837.50	1,827.70	1,782.80
Accumulated depreciation, depletion and amortization	-687.9	-673.9	-640.6
Net Property, Plant and Equipment	1,149.60	1,153.80	1,142.20
Investment in unconsolidated affiliate	24.5	24.7	25.2
Noncurrent regulatory and other assets	10.4	10.8	11.3
TOTAL ASSETS	1,304	1,311.70	1,300.10
Current Liabilities
Accounts payable and accrued expenses	33.9	21.7	38.7
Accounts payable to affiliates	3.4	5.8	3.4
Dividends payable to Questar	0	16	0
Current regulatory liabilities	0.9	0.9	2
Current portion of long-term debt and capital lease obligation	25.1	25.1	0
Total Current Liabilities	63.3	69.5	44.1
Long-term debt and capital lease obligation, less current portion	433.7	433.7	458.8
Deferred income taxes	241.3	241.4	228.6
Noncurrent regulatory and other liabilities	16	15.9	15.9
COMMON SHAREHOLDERS' EQUITY
Common stock	6.6	6.6	6.6
Additional paid-in capital	351.9	351.4	350.1
Retained earnings	213.6	215.7	218.8
Accumulated other comprehensive (loss)	-22.4	-22.5	-22.8
Total Common Shareholders' Equity	549.7	551.2	552.7
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	$1,304	$1,311.70	$1,300.10

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
OPERATING ACTIVITIES
Net income	$84.60	$85.10
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	56.2	57.2
Deferred income taxes	-3.8	-1.2
Share-based compensation	3.2	3.2
(Income) from unconsolidated affiliate	-0.9	-0.9
Distributions from unconsolidated affiliate and other	1.5	1.6
Changes in operating assets and liabilities	82.6	67.9
Net Cash Provided By Operating Activities	223.4	212.9
INVESTING ACTIVITIES
Property, plant and equipment	-66.1	-69.7
Questar Gas acquisition of gas distribution system	-11.4	0
Cash used in disposition of assets	-0.6	-0.9
Proceeds from disposition of assets	0.2	0
Net Cash Used In Investing Activities	-77.9	-70.6
FINANCING ACTIVITIES
Common stock issued	1.3	0.5
Common stock repurchased	-3.6	-2.8
Change in short-term debt	-133	-119
Capital lease obligation repaid	0.3	0.3
Dividends paid	-37.1	-31.6
Tax benefits from share-based compensation	0	0.5
Net Cash Provided By (Used In) Financing Activities	-172.7	-152.7
Change in cash and cash equivalents	-27.2	-10.4
Beginning cash and cash equivalents	32	16
Ending cash and cash equivalents	4.8	5.6
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	43.8	39.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.9	14.6
Deferred income taxes	-2.4	-0.1
Share-based compensation	0.3	0.3
Changes in operating assets and liabilities	80	45.3
Net Cash Provided By Operating Activities	136.6	99.7
INVESTING ACTIVITIES
Property, plant and equipment	-43	-48.9
Questar Gas acquisition of gas distribution system	-11.4	0
Cash used in disposition of assets	-0.5	-0.9
Proceeds from disposition of assets	0.1	0
Net Cash Used In Investing Activities	-54.8	-49.8
FINANCING ACTIVITIES
Change in notes receivable from Questar	0	-30.6
Change in notes payable to Questar	-83.5	-17.7
Checks outstanding in excess of cash balances	0.4	0
Dividends paid to Questar	-18.5	-9
Net Cash Provided By (Used In) Financing Activities	-101.6	-57.3
Change in cash and cash equivalents	-19.8	-7.4
Beginning cash and cash equivalents	19.8	8.8
Ending cash and cash equivalents	0	1.4
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	13.9	15.7
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.5	14.1
Deferred income taxes	-0.2	-0.1
Share-based compensation	0.5	0.6
(Income) from unconsolidated affiliate	-0.9	-0.9
Distributions from unconsolidated affiliate and other	1.3	1.5
Changes in operating assets and liabilities	6.2	13
Net Cash Provided By Operating Activities	35.3	43.9
INVESTING ACTIVITIES
Property, plant and equipment	-8.7	-8.5
Cash used in disposition of assets	-0.1	0
Net Cash Used In Investing Activities	-8.8	-8.5
FINANCING ACTIVITIES
Change in notes receivable from Questar	4.2	-17.2
Dividends paid to Questar	-32	-16
Net Cash Provided By (Used In) Financing Activities	-27.8	-33.2
Change in cash and cash equivalents	-1.3	2.2
Beginning cash and cash equivalents	7.4	2.7
Ending cash and cash equivalents	$6.10	$4.90

Nature_of_Business_Notes

Nature of Business (Notes)	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Note 1 - Nature of Business
	Questar Corporation is a Rockies-based integrated natural gas company with three principal complementary and wholly-owned lines of business:
	•	Questar Gas Company (Questar Gas) provides retail natural gas distribution in Utah, Wyoming and Idaho.
	•	Wexpro Company (Wexpro) develops and produces natural gas from cost-of-service reserves for Questar Gas customers.
	•	Questar Pipeline Company (Questar Pipeline) operates interstate natural gas pipelines and storage facilities in the western United States and provides other energy services.
	Questar is headquartered in Salt Lake City, Utah. Shares of Questar common stock trade on the New York Stock Exchange (NYSE:STR).

Basis_of_Presentation_of_Inter

Basis of Presentation of Interim Financial Statements (Notes)	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation of Interim Financial Statements	Note 2 - Basis of Presentation of Interim Financial Statements
	The interim financial statements contain the accounts of Questar and its wholly-owned subsidiaries. The financial statements were prepared in accordance with U.S. generally accepted accounting principles (GAAP), the instructions for Quarterly Reports on Form 10-Q and SEC Regulations S-X and S-K. All significant intercompany accounts and transactions have been eliminated in consolidation.
	The financial statements reflect all normal, recurring adjustments and accruals that are, in the opinion of management, necessary for a fair presentation of financial position and results of operations for the interim periods presented. Interim financial statements do not include all of the information and notes required by GAAP for audited annual financial statements. These financial statements should be read in conjunction with the financial statements and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2014.
	The preparation of financial statements and notes in conformity with GAAP requires that management make estimates and assumptions that affect the amounts of revenues, expenses, assets and liabilities, and disclosure of contingent assets and liabilities. Actual results could differ from estimates. The results of operations for the three and 12 months ended March 31, 2015, are not necessarily indicative of the results that may be expected for the year ending December 31, 2015.
	Certain reclassifications were made to prior year information to conform to the current year presentation.
	Questar and Questar Pipeline use the equity method to account for an investment in an unconsolidated affiliate where they do not have control, but have significant influence. The investment in the unconsolidated affiliate on the Condensed Consolidated Balance Sheets equals Questar Pipeline's proportionate share of equity reported by the unconsolidated affiliate. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below the Questar Pipeline's carrying value. When such a condition is deemed to be other-than-temporary, the carrying value of the investment is written down to its fair value, and the amount of the write-down is included in the determination of net income. White River Hub, LLC, a limited liability company and FERC-regulated transporter of natural gas, is the sole unconsolidated affiliate. Questar Pipeline owns 50% of White River Hub, LLC, and is the operator.
	In March 2015, Questar Gas purchased Eagle Mountain City's municipal natural gas system for $11.4 million. The city has over 6,500 natural gas customers and is one of Utah's fastest-growing areas.
	Questar Gas obtains the majority of its gas supply from Wexpro's cost-of-service production and pays Wexpro an operator service fee based on the terms of the Wexpro Agreement and the Wexpro II Agreement (Wexpro agreements). Questar Gas also obtains transportation and storage services from Questar Pipeline. These intercompany revenues and expenses are eliminated in the Questar Consolidated Statements of Income by reducing revenues and cost of sales. The underlying costs of Wexpro's production and Questar Pipeline's transportation and storage services are disclosed in other categories in the Consolidated Statements of Income, including operating and maintenance expense and depreciation, depletion and amortization expense. During the second and third quarters of the year, a significant portion of the natural gas from Wexpro production is injected into underground storage. This gas is withdrawn from storage as needed during the heating season in the first and fourth quarters. The cost of natural gas sold is credited with the value of natural gas as it is injected into storage and debited as it is withdrawn from storage. The reported balance in consolidated cost of sales may be a negative amount during the second and third quarters because of the entries to record injection of gas into storage and the elimination of intercompany transactions. The details of Questar's consolidated cost of sales are as follows:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Questar Gas
	Gas purchases	$	41		$	92.7		$	84.8		$	176
	Operator service fee	84.8			89.1			345.4			310.9
	Transportation and storage	22.2			22.1			79.7			80.2
	Gathering	5.4			4.9			21.5			19.1
	Royalties	11.9			17.3			54.7			50.5
	Storage (injection) withdrawal, net	30.9			33			(3.2		)	3.4
	Purchased-gas account adjustment	36.2			(5.6		)	(4.0		)	(30.3		)
	Other	1.2			1.1			4.9			4.8
	Total Questar Gas cost of natural gas sold	233.6			254.6			583.8			614.6
	Elimination of Questar Gas cost of natural gas sold - affiliated companies	(104.0		)	(108.2		)	(419.2		)	(387.0		)
	Total Questar Gas cost of natural gas sold - unaffiliated parties	129.6			146.4			164.6			227.6
	Questar Pipeline
	Total Questar Pipeline cost of sales	1.9			1.7			4.2			6.6
	Other cost of sales	0.3			0.1			1.1			0.2
	Total cost of sales	$	131.8		$	148.2		$	169.9		$	234.4

Earnings_Per_Share_Notes

Earnings Per Share (Notes)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Share	Note 3 - Earnings Per Share
	Basic earnings per share (EPS) is computed by dividing net income by the weighted-average number of common shares outstanding during the reporting period, which includes vested undistributed restricted stock units (RSUs). Diluted EPS includes the potential increase in the number of outstanding shares that could result from the exercise of in-the-money stock options, the vesting of RSUs with forfeitable dividend equivalents and the distribution of performance shares that are part of the Company's Long-Term Stock Incentive Plan (LTSIP), less shares repurchased under the treasury stock method. Restricted shares and RSUs with nonforfeitable dividends or dividend equivalents are participating securities for the computation of basic EPS under the two-class method. The application of the two-class method has an insignificant impact on the calculation of Questar's basic and diluted EPS. A reconciliation of the components of basic and diluted shares used in the EPS calculation follows:
		3 Months Ended		12 Months Ended
		March 31,		March 31,
		2015	2014	2015	2014
		(in millions)
	Weighted-average basic common shares outstanding	176.2	175.7	176	175.6
	Potential number of shares issuable under the Company's LTSIP	0.3	0.4	0.3	0.5
	Weighted-average diluted common shares outstanding	176.5	176.1	176.3	176.1

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Notes)	3 Months Ended
	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Accumulated Other Comprehensive Income	Note 4 - Accumulated Other Comprehensive Income
	Comprehensive income, as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Consolidated Statements of Income and net other comprehensive income (loss) (OCI). OCI includes recognition of the under-funded position of pension and other postretirement benefit plans, interest rate cash flow hedges, changes in the fair value of long-term investment, and the related income taxes. Income or loss is recognized when the pension and other postretirement benefit (OPB) costs are accrued, as the Company records interest expense for hedged interest payments and when the long-term investment is sold.
	Details of the changes in the components of consolidated accumulated other comprehensive income (loss) (AOCI), net of income taxes, as reported in Questar's Condensed Consolidated Balance Sheets, are shown in the tables below. The tables also disclose details of income taxes related to each component of OCI.
		Pension and OPB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPB			Interest rate cash flow hedges			Long-term invest.			Total
		3 Months Ended March 31,											3 Months Ended March 31,
		March 31, 2015											March 31, 2014
		(in millions)
	AOCI at beginning of period	$	(178.9	)	$	(22.5	)	$	0.1	$	(201.3	)	$	(119.0	)	$	(22.9	)	$	0.1		$	(141.8	)
	Reclassified from AOCI(1)	6			0.2			—		6.2			4.3			0.2			—			4.5
	Income taxes
	Reclassified from AOCI(2)	(2.3		)	(0.1		)	—		(2.4		)	(1.7		)	(0.1		)	—			(1.8		)
	Net other comprehensive income	3.7			0.1			—		3.8			2.6			0.1			—			2.7
	AOCI at end of period	$	(175.2	)	$	(22.4	)	$	0.1	$	(197.5	)	$	(116.4	)	$	(22.8	)	$	0.1		$	(139.1	)
		Pension and OPB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPB			Interest rate cash flow hedges			Long-term invest.			Total
		12 Months Ended											12 Months Ended
		March 31, 2015											March 31, 2014
		(in millions)
	AOCI at beginning of period	$	(116.4	)	$	(22.8	)	$	0.1	$	(139.1	)	$	(218.3	)	$	(23.1	)	$	0.1		$	(241.3	)
	OCI before reclassifications	(113.6		)	—			—		(113.6		)	135.8			—			(0.1		)	135.7
	Reclassified from AOCI(1)	18.4			0.5			—		18.9			29.5			0.5			—			30
	Income taxes
	OCI before reclassifications	43.4			—			—		43.4			(51.9		)	—			0.1			(51.8		)
	Reclassified from AOCI(2)	(7.0		)	(0.1		)	—		(7.1		)	(11.5		)	(0.2		)	—			(11.7		)
	Total income taxes	36.4			(0.1		)	—		36.3			(63.4		)	(0.2		)	0.1			(63.5		)
	Net other comprehensive income (loss)	(58.8		)	0.4			—		(58.4		)	101.9			0.3			—			102.2
	AOCI at end of period	$	(175.2	)	$	(22.4	)	$	0.1	$	(197.5	)	$	(116.4	)	$	(22.8	)	$	0.1		$	(139.1	)
	(1) Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income.
	(2) Income tax reclassifications related to interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income.
	Pension and other postretirement benefit AOCI reclassifications are included in the computation of net periodic pension and postretirement benefit costs. See Note 9 for additional details.
	Comprehensive income, as reported in Questar Pipeline's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Pipeline Consolidated Statements of Income and net OCI. OCI includes interest rate cash flow hedges and the related income taxes. Income or loss is recognized as the company records interest expense for hedged interest payments. Disclosures above regarding interest rate cash flow hedges, including related income taxes and income statement reclassification effects, apply to Questar Pipeline.

Asset_Retirement_Obligations_N

Asset Retirement Obligations (Notes)	3 Months Ended
	Mar. 31, 2015
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	Note 5 - Asset Retirement Obligations
	Questar records an asset retirement obligation (ARO) along with an increase to the carrying value of the related property, plant and equipment when there is a legal obligation associated with the retirement of a tangible long-lived asset. Questar's AROs apply primarily to abandonment costs associated with gas and oil wells, production facilities and certain other properties. The Company has not recorded AROs on a majority of its long-lived transportation and distribution assets because the Company does not have a legal obligation to restore the area surrounding abandoned assets. The fair value of retirement costs is estimated by Company personnel based on abandonment costs of similar properties available to field operations and depreciated over the life of the related assets. Revisions to estimates result from material changes in the expected timing or amount of cash flows associated with AROs. Income or expense resulting from the settlement of ARO liabilities is included in net gain (loss) from asset sales on the Consolidated Statements of Income. The ARO liability is adjusted to present value each period through an accretion calculation using a credit-adjusted risk-free interest rate. Changes in Questar's AROs from the Condensed Consolidated Balance Sheets were as follows:
		3 Months Ended
		March 31,
		2015			2014
		(in millions)
	AROs at beginning of year	$	69.3		$	67.7
	Accretion	0.8			0.8
	Liabilities incurred	0.1			0.4
	Revisions in estimated cash flows	5.7			0.4
	Liabilities settled	(0.9		)	(0.7		)
	AROs at end of period	$	75		$	68.6
	Wexpro collects from Questar Gas and deposits in trust certain funds related to AROs. The funds are recorded as other noncurrent assets and used to satisfy retirement obligations as the properties are abandoned. The accounting treatment of reclamation activities associated with AROs for properties administered under the Wexpro agreements is defined in a guideline letter between Wexpro and the Utah Division of Public Utilities and the staff of the Wyoming Public Service Commission.

Fair_Value_Measurements_Notes

Fair Value Measurements (Notes)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 6 - Fair Value Measurements
	Questar complies with the accounting standards for fair value measurements and disclosures. The standards establish a fair value hierarchy. Level 1 inputs are unadjusted quoted prices for identical assets or liabilities in active markets that the Company has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 inputs are unobservable inputs for the asset or liability. The Company had no assets or liabilities measured using Level 3 inputs at March 31, 2015, March 31, 2014 or December 31, 2014. Fair value accounting standards also apply to certain nonfinancial assets and liabilities that are measured at fair value on a nonrecurring basis. Questar did not have any such assets or liabilities at March 31, 2015, March 31, 2014 or December 31, 2014.
	Questar
	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar's financial statements in this Quarterly Report:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Mar. 31, 2015				Mar. 31, 2014				Dec. 31, 2014
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	4.8	$	4.8	$	5.6	$	5.6	$	32	$	32
	Long-term investment	1	16.2		16.2		15.3		15.3		15.7		15.7
	Financial liabilities
	Short-term debt	1	214		214		157		157		347		347
	Long-term debt, including current portion	2	1,244.80		1,396.30		1,246.60		1,357.50		1,245.20		1,356.10
	The long-term investment is recorded at fair value and consists of money market and short-term bond index mutual funds held in Wexpro's trust (see Note 5). The fair value of the long-term investment is based on quoted prices for the underlying funds. The fair value of fixed-rate long-term debt is based on the discounted present value of cash flows using the Company's current credit risk-adjusted borrowing rates.
	Questar Gas
	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Gas's financial statements in this Quarterly Report:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Mar. 31, 2015				Mar. 31, 2014				Dec. 31, 2014
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	1.4	$	1.4	$	19.8	$	19.8
	Notes receivable from Questar	1	—		—		30.6		30.6		—		—
	Financial liabilities
	Checks outstanding in excess of cash balances	1	0.4		0.4		—		—		—		—
	Notes payable to Questar	1	35.8		35.8		—		—		119.3		119.3
	Long-term debt	2	534.5		629		534.5		588.9		534.5		607.2
	The carrying amounts of notes receivable from and notes payable to Questar approximate fair value because of their short maturities and market-based interest rates. The fair value of fixed-rate long-term debt is based on the discounted present value of cash flows using Questar Gas's current credit risk-adjusted borrowing rates.
	Questar Pipeline
	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Pipeline's financial statements in this Quarterly Report:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Mar. 31, 2015				Mar. 31, 2014				Dec. 31, 2014
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	6.1	$	6.1	$	4.9	$	4.9	$	7.4	$	7.4
	Notes receivable from Questar	1	35.9		35.9		46.6		46.6		40.1		40.1
	Financial liabilities
	Long-term debt, including current portion	2	458.8		515.1		458.8		509.4		458.8		495.5
	The carrying amounts of notes receivable from Questar approximate fair value because of their short maturities and market-based interest rates. The fair value of fixed-rate long-term debt is based on the discounted present value of cash flows using Questar Pipeline's current credit risk-adjusted borrowing rates.

Derivatives_and_Hedging_Notes

Derivatives and Hedging (Notes)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging	Note 7 - Derivatives and Hedging
	Questar and its subsidiaries may enter into derivative instruments to manage exposure to changes in current and future market interest rates. Questar Pipeline entered into forward starting swaps totaling $150.0 million in the second and third quarters of 2011 in anticipation of issuing $180.0 million of notes in December 2011. Settlement of these swaps required payments of $37.3 million in the fourth quarter of 2011 because of declines in interest rates. These swaps qualified as cash flow hedges and the settlement payments are being amortized to interest expense over the 30-year life of the debt. See the Condensed Consolidated Statements of Comprehensive Income and Note 4 for details regarding reclassifications of AOCI related to deferred interest rate cash flow hedge losses to interest expense for the three and 12 months ended March 31, 2015 and March 31, 2014.
	Reclassifications into earnings of amounts reported in AOCI will continue while interest expense is recorded for the hedged interest payments through maturity in 2041. Pre-tax net losses of $0.6 million are expected to be reclassified from AOCI to the Consolidated Statements of Income in the next 12 months. As of March 31, 2015, the Company was not hedging any exposure to variability in future cash flows of forecasted transactions. There were no derivative assets or liabilities outstanding at March 31, 2015, March 31, 2014 or December 31, 2014.

Operations_by_Line_of_Business

Operations by Line of Business (Notes)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Operations by Line of Business	Note 8 - Operations by Line of Business
	Questar's three principal complementary lines of business include Questar Gas, which provides retail natural gas distribution in Utah, Wyoming and Idaho; Wexpro, which develops and produces natural gas from cost-of-service reserves for Questar Gas customers; and Questar Pipeline, which operates interstate natural gas pipelines and storage facilities and provides other energy services. Line-of-business information is presented according to senior management's basis for evaluating performance and considering differences in the nature of products, services and regulation, among other factors.
	Following is a summary of operations by line of business:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Revenues from Unaffiliated Customers
	Questar Gas	$	374.8		$	396.3		$	939.4		$	963.2
	Wexpro	6.3			12.3			29.6			47.1
	Questar Pipeline	46.8			48			189			189.2
	Other	0.7			0.3			3			0.5
	Total	$	428.6		$	456.9		$	1,161.00		$	1,200.00
	Revenues from Affiliated Companies
	Questar Gas	$	—		$	—		$	—		$	0.3
	Wexpro	84.8			89.1			346			311.1
	Questar Pipeline	19.4			19.3			73.8			76.5
	Total	$	104.2		$	108.4		$	419.8		$	387.9
	Operating Income (Loss)
	Questar Gas	$	76.6		$	69.8		$	116.3		$	107.4
	Wexpro	41.7			48.5			176.5			176.4
	Questar Pipeline	27.4			30.1			114.9			35.4
	Corporate and other	1.3			(0.1		)	(3.6		)	3.5
	Total	$	147		$	148.3		$	404.1		$	322.7
	Net Income (Loss)
	Questar Gas	$	43.8		$	39.6		$	59.4		$	55.4
	Wexpro	27.7			31.8			118.7			116.1
	Questar Pipeline	13.9			15.7			58.8			8.1
	Corporate and other	(0.8		)	(2.0		)	(10.9		)	(6.2		)
	Total	$	84.6		$	85.1		$	226		$	173.4

Employee_Benefits_Notes

Employee Benefits (Notes)	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee Benefits	Note 9 - Employee Benefits
	The Company has a noncontributory defined benefit pension plan covering a majority of its employees and postretirement medical and life insurance plans providing coverage to less than half of its employees. Employees hired or rehired after June 30, 2010, are not eligible for the noncontributory defined benefit pension plan and employees hired or rehired after December 31, 1996, are not eligible for the postretirement medical plan and are not eligible to receive basic life insurance once they retire.
	Questar is subject to and complies with minimum-required and maximum-allowed annual contribution levels for its qualified pension plan, as determined by the Employee Retirement Income Security Act and the Internal Revenue Code. The 2015 estimated net cost for the qualified pension plan is $18.9 million.
	The Company also has a nonqualified pension plan that covers a group of management employees in addition to the noncontributory qualified pension plan. The nonqualified pension plan provides for defined benefit payments upon retirement of the management employee, or to the spouse upon death of the management employee, above the benefit limit defined by the Internal Revenue Service (IRS) for the qualified plan. The nonqualified pension plan is unfunded; benefits are paid from the Company's general funds. The 2015 estimated net cost for the nonqualified pension plan is $3.4 million.
	Components of the qualified and nonqualified net periodic pension cost are listed in the table below:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Service cost	$	3.4		$	3		$	12.2		$	13.4
	Interest cost	8.1			8.4			33.1			31.2
	Expected return on plan assets	(11.6		)	(10.6		)	(44.6		)	(39.2		)
	Prior service cost	—			0.1			0.5			0.9
	Recognized net actuarial loss	5.7			3.9			17.2			26
	Net pension cost	$	5.6		$	4.8		$	18.4		$	32.3
	The Company currently estimates a $2.2 million net cost for postretirement benefits other than pensions in 2015, before accretion of a regulatory liability. Net periodic postretirement benefit cost components are listed in the table below:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Service cost	$	0.2		$	0.2		$	0.6		$	0.7
	Interest cost	0.9			1			3.7			3.7
	Expected return on plan assets	(0.8		)	(0.8		)	(3.0		)	(2.7		)
	Recognized net actuarial loss (gain)	0.3			0.3			0.7			2.6
	Accretion of regulatory liability	0.2			0.2			0.8			0.5
	Net postretirement benefit cost	$	0.8		$	0.9		$	2.8		$	4.8

Contingencies_Notes

Contingencies (Notes)	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Note 10 - Contingencies
	Questar and each of its subsidiaries are involved in various commercial, environmental, and regulatory claims. Litigation and other legal proceedings arise in the ordinary course of business. Except as stated below concerning the QEP lawsuit, management does not believe any litigation or other legal proceedings individually or in the aggregate will have a material adverse effect on Questar's, Questar Gas's or Questar Pipeline's financial position, results of operations or cash flows.
	A liability is recorded for a loss contingency when its occurrence is probable and its amount can be reasonably estimated. If some amount within a range of possible outcomes appears to be a better estimate than any other amount within the range, that amount is recorded. Otherwise, the minimum amount in the range is recorded. Disclosures are provided for contingencies reasonably likely to occur, which would have a material adverse effect on Questar's, Questar Gas's or Questar Pipeline's financial position, results of operations or cash flows. Some of the claims involve highly complex issues relating to liability, damages and other matters subject to substantial uncertainties and, therefore, the probability of liability or an estimate of loss cannot be reasonably determined.
	Litigation
	On May 1, 2012, Questar Gas Company filed a legal action against QEP Field Services Company, a subsidiary of QEP Resources, Inc. The case, entitled Questar Gas Company v. QEP Field Services Company, was filed in the Third District Court in Salt Lake County, Utah. Questar Gas believes certain charges of QEP Field Services Company for gathering services exceed the amounts contemplated under a Gas Gathering Agreement, effective September 1, 1993, pertaining to certain gas produced by Wexpro Company under the Wexpro Agreement. Questar Gas is alleging breach of contract by QEP Field Services Company and is seeking an accounting, damages and a declaratory judgment relating to the services and charges under the Gas Gathering Agreement. The charges under the Gas Gathering Agreement are included in Questar Gas's rates as part of its purchased-gas costs. QEP Field Services Company filed an answer and counterclaim alleging that Questar Gas breached the Agreement by failing to allow QEP Field Services to gather and process gas from certain wells located in two fields in the state of Wyoming.
	On August 13, 2013, QEP Field Services Company assigned its interest in the Gas Gathering Agreement to QEPM Gathering I, LLC, a subsidiary of the general partner of the master limited partnership QEP Midstream Partners. Plaintiffs have filed an amended complaint naming QEP Midstream Partners, LP; QEP Midstream Partners GP, LLC; QEP Midstream Partners Operating, LLC; and QEPM Gathering I, LLC (QEP MLP Entities). QEP Field Services and Tesoro Logistics LP (Tesoro) entered into a Membership Interest Purchase Agreement dated October 19, 2014, to transfer QEP Field Services’ interest in the QEP MLP Entities and related assets and liabilities of QEP Field Services to Tesoro, including control of this legal action. Tesoro closed on the transaction for QEP’s midstream business on December 2, 2014.
	On December 2, 2014, the court issued a memorandum decision granting two motions for partial summary judgment for breach of contract filed by Questar Gas. The court found QEP Field Services Company breached the Gas Gathering Agreement by overcharging Questar Gas in its gathering rates. The court also denied two motions for partial summary judgment filed by QEP Field Services to reduce or limit contract damages. The court also denied cross-motions for partial summary judgment filed by both parties relating to another claim of breach of contract. The issues raised by the cross-motions, QEP Field Services’ counterclaim and damages on all claims are currently reserved for trial. Trial has been scheduled for September 8 through 18, 2015.
	While Questar Gas intends to vigorously pursue its legal rights, the claims and counterclaims involve complex legal issues and uncertainties that make it difficult to predict the outcome of the case and therefore management cannot determine at this time whether this litigation may have a material adverse effect on its financial position, results of operations or cash flows.
	In February 2015, a trial was held in the case of Rocky Mountain Resources and Robert N. Floyd v. QEP Energy Company and Wexpro Company, Ninth Judicial District, County of Sublette, State of Wyoming, Case No. 2011-7816. Plaintiffs allege they are entitled to a 4% overriding royalty interest (ORRI) in a so-called replacement state oil and gas lease ultimately assigned to Wexpro and QEP Energy Company (QEP) in the Pinedale Field. Wexpro and QEP believe the former state leases subject to the ORRI expired and a new lease was issued by the State of Wyoming unburdened by the 4% ORRI. A jury decision was reached on February 13, 2015, that awarded the Plaintiffs $14.1 million from Wexpro and $16.2 million from QEP. Wexpro and QEP plan to file an appeal of the case to the Wyoming Supreme Court. Wexpro has accrued its estimate of liability in the case. Any additional royalties will be recovered from Questar Gas’s customers.

Asset_Impairments_Notes

Asset Impairments (Notes)	3 Months Ended
	Mar. 31, 2015
Strategic Review of Questar Southern Trails Pipeline and Impairment of Eastern Segment [Abstract]
Asset Impairments	Note 11 - Asset Impairments
	During the second quarter of 2014, Wexpro recorded a pre-tax abandonment and impairment charge of $2.0 million for its share of the remaining investment in the Brady field. Wexpro concluded that the field had reached the end of its productive life because it was no longer economical to produce natural gas and oil.
	During the third quarter of 2013, Questar Pipeline updated its five-year forecast for the eastern segment of Southern Trails Pipeline, which resulted in revised projections of higher operating expenses, including right-of-way and pipeline safety costs. Current and projected market rates for natural gas transportation between the San Juan Basin and California markets did not cover these increasing operating expenses. Because of changes in expected cash flows in the third quarter of 2013 and the lack of progress in selling or recontracting this pipeline, Questar Pipeline recorded a noncash impairment of its entire investment in the eastern segment of Southern Trails Pipeline of $80.6 million, or $52.4 million after income taxes. Questar Pipeline used a probability-weighted discounted cash flow analysis that included significant inputs such as Questar Pipeline's cost of capital and assumptions regarding future transportation rates and operating costs.

Recent_Accounting_Developments

Recent Accounting Developments (Notes)	3 Months Ended
	Mar. 31, 2015
Recent Accounting Developments [Abstract]
Recent Accounting Developments	Note 12 - Recent Accounting Developments
	In April 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-03, Interest - Imputation of Interest (Subtopic 835-30). The ASU simplifies the presentation of debt issuance costs by requiring that the debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. The guidance will be effective beginning January 1, 2016. Early adoption is permitted. The new guidance must be applied retrospectively to each prior period presented. The Company is currently evaluating the ASU's effect on its financial position.
	In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). The ASU replaces most of the existing revenue guidance with a single set of principles, including changes in recognition and disclosure requirements. The guidance will be effective beginning January 1, 2017. Early adoption is not permitted. The new guidance must be applied retrospectively to each prior period presented or via a cumulative effect upon the date of initial application. The Company is currently evaluating the ASU's effect on its financial position, results of operations or cash flows, as well as which transition approach it will take.

Basis_of_Presentation_of_Inter1

Basis of Presentation of Interim Financial Statements (Policies)	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Questar Corporation is a Rockies-based integrated natural gas company with three principal complementary and wholly-owned lines of business:
	•	Questar Gas Company (Questar Gas) provides retail natural gas distribution in Utah, Wyoming and Idaho.
	•	Wexpro Company (Wexpro) develops and produces natural gas from cost-of-service reserves for Questar Gas customers.
	•	Questar Pipeline Company (Questar Pipeline) operates interstate natural gas pipelines and storage facilities in the western United States and provides other energy services.
	Questar is headquartered in Salt Lake City, Utah. Shares of Questar common stock trade on the New York Stock Exchange (NYSE:STR).
Investment in Unconsolidated Affiliate	Questar and Questar Pipeline use the equity method to account for an investment in an unconsolidated affiliate where they do not have control, but have significant influence. The investment in the unconsolidated affiliate on the Condensed Consolidated Balance Sheets equals Questar Pipeline's proportionate share of equity reported by the unconsolidated affiliate. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below the Questar Pipeline's carrying value. When such a condition is deemed to be other-than-temporary, the carrying value of the investment is written down to its fair value, and the amount of the write-down is included in the determination of net income. White River Hub, LLC, a limited liability company and FERC-regulated transporter of natural gas, is the sole unconsolidated affiliate. Questar Pipeline owns 50% of White River Hub, LLC, and is the operator.
Earnings Per Share	Basic earnings per share (EPS) is computed by dividing net income by the weighted-average number of common shares outstanding during the reporting period, which includes vested undistributed restricted stock units (RSUs). Diluted EPS includes the potential increase in the number of outstanding shares that could result from the exercise of in-the-money stock options, the vesting of RSUs with forfeitable dividend equivalents and the distribution of performance shares that are part of the Company's Long-Term Stock Incentive Plan (LTSIP), less shares repurchased under the treasury stock method. Restricted shares and RSUs with nonforfeitable dividends or dividend equivalents are participating securities for the computation of basic EPS under the two-class method. The application of the two-class method has an insignificant impact on the calculation of Questar's basic and diluted EPS.
Comprehensive Income - Questar	Comprehensive income, as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Consolidated Statements of Income and net other comprehensive income (loss) (OCI). OCI includes recognition of the under-funded position of pension and other postretirement benefit plans, interest rate cash flow hedges, changes in the fair value of long-term investment, and the related income taxes. Income or loss is recognized when the pension and other postretirement benefit (OPB) costs are accrued, as the Company records interest expense for hedged interest payments and when the long-term investment is sold.
Comprehensive Income - Questar Pipeline	Comprehensive income, as reported in Questar Pipeline's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Pipeline Consolidated Statements of Income and net OCI. OCI includes interest rate cash flow hedges and the related income taxes. Income or loss is recognized as the company records interest expense for hedged interest payments.
Asset Retirement Obligations	Questar records an asset retirement obligation (ARO) along with an increase to the carrying value of the related property, plant and equipment when there is a legal obligation associated with the retirement of a tangible long-lived asset. Questar's AROs apply primarily to abandonment costs associated with gas and oil wells, production facilities and certain other properties. The Company has not recorded AROs on a majority of its long-lived transportation and distribution assets because the Company does not have a legal obligation to restore the area surrounding abandoned assets. The fair value of retirement costs is estimated by Company personnel based on abandonment costs of similar properties available to field operations and depreciated over the life of the related assets. Revisions to estimates result from material changes in the expected timing or amount of cash flows associated with AROs. Income or expense resulting from the settlement of ARO liabilities is included in net gain (loss) from asset sales on the Consolidated Statements of Income. The ARO liability is adjusted to present value each period through an accretion calculation using a credit-adjusted risk-free interest rate.
Business Segments	Line-of-business information is presented according to senior management's basis for evaluating performance and considering differences in the nature of products, services and regulation, among other factors.
Contingencies	A liability is recorded for a loss contingency when its occurrence is probable and its amount can be reasonably estimated. If some amount within a range of possible outcomes appears to be a better estimate than any other amount within the range, that amount is recorded. Otherwise, the minimum amount in the range is recorded. Disclosures are provided for contingencies reasonably likely to occur, which would have a material adverse effect on Questar's, Questar Gas's or Questar Pipeline's financial position, results of operations or cash flows. Some of the claims involve highly complex issues relating to liability, damages and other matters subject to substantial uncertainties and, therefore, the probability of liability or an estimate of loss cannot be reasonably determined.

Basis_of_Presentation_of_Inter2

Basis of Presentation of Interim Financial Statements (Tables)	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cost of sales detail	The details of Questar's consolidated cost of sales are as follows:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Questar Gas
	Gas purchases	$	41		$	92.7		$	84.8		$	176
	Operator service fee	84.8			89.1			345.4			310.9
	Transportation and storage	22.2			22.1			79.7			80.2
	Gathering	5.4			4.9			21.5			19.1
	Royalties	11.9			17.3			54.7			50.5
	Storage (injection) withdrawal, net	30.9			33			(3.2		)	3.4
	Purchased-gas account adjustment	36.2			(5.6		)	(4.0		)	(30.3		)
	Other	1.2			1.1			4.9			4.8
	Total Questar Gas cost of natural gas sold	233.6			254.6			583.8			614.6
	Elimination of Questar Gas cost of natural gas sold - affiliated companies	(104.0		)	(108.2		)	(419.2		)	(387.0		)
	Total Questar Gas cost of natural gas sold - unaffiliated parties	129.6			146.4			164.6			227.6
	Questar Pipeline
	Total Questar Pipeline cost of sales	1.9			1.7			4.2			6.6
	Other cost of sales	0.3			0.1			1.1			0.2
	Total cost of sales	$	131.8		$	148.2		$	169.9		$	234.4

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Schedule of Weighted Average Number of Shares	A reconciliation of the components of basic and diluted shares used in the EPS calculation follows:
		3 Months Ended		12 Months Ended
		March 31,		March 31,
		2015	2014	2015	2014
		(in millions)
	Weighted-average basic common shares outstanding	176.2	175.7	176	175.6
	Potential number of shares issuable under the Company's LTSIP	0.3	0.4	0.3	0.5
	Weighted-average diluted common shares outstanding	176.5	176.1	176.3	176.1

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	Details of the changes in the components of consolidated accumulated other comprehensive income (loss) (AOCI), net of income taxes, as reported in Questar's Condensed Consolidated Balance Sheets, are shown in the tables below. The tables also disclose details of income taxes related to each component of OCI.
		Pension and OPB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPB			Interest rate cash flow hedges			Long-term invest.			Total
		3 Months Ended March 31,											3 Months Ended March 31,
		March 31, 2015											March 31, 2014
		(in millions)
	AOCI at beginning of period	$	(178.9	)	$	(22.5	)	$	0.1	$	(201.3	)	$	(119.0	)	$	(22.9	)	$	0.1		$	(141.8	)
	Reclassified from AOCI(1)	6			0.2			—		6.2			4.3			0.2			—			4.5
	Income taxes
	Reclassified from AOCI(2)	(2.3		)	(0.1		)	—		(2.4		)	(1.7		)	(0.1		)	—			(1.8		)
	Net other comprehensive income	3.7			0.1			—		3.8			2.6			0.1			—			2.7
	AOCI at end of period	$	(175.2	)	$	(22.4	)	$	0.1	$	(197.5	)	$	(116.4	)	$	(22.8	)	$	0.1		$	(139.1	)
		Pension and OPB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPB			Interest rate cash flow hedges			Long-term invest.			Total
		12 Months Ended											12 Months Ended
		March 31, 2015											March 31, 2014
		(in millions)
	AOCI at beginning of period	$	(116.4	)	$	(22.8	)	$	0.1	$	(139.1	)	$	(218.3	)	$	(23.1	)	$	0.1		$	(241.3	)
	OCI before reclassifications	(113.6		)	—			—		(113.6		)	135.8			—			(0.1		)	135.7
	Reclassified from AOCI(1)	18.4			0.5			—		18.9			29.5			0.5			—			30
	Income taxes
	OCI before reclassifications	43.4			—			—		43.4			(51.9		)	—			0.1			(51.8		)
	Reclassified from AOCI(2)	(7.0		)	(0.1		)	—		(7.1		)	(11.5		)	(0.2		)	—			(11.7		)
	Total income taxes	36.4			(0.1		)	—		36.3			(63.4		)	(0.2		)	0.1			(63.5		)
	Net other comprehensive income (loss)	(58.8		)	0.4			—		(58.4		)	101.9			0.3			—			102.2
	AOCI at end of period	$	(175.2	)	$	(22.4	)	$	0.1	$	(197.5	)	$	(116.4	)	$	(22.8	)	$	0.1		$	(139.1	)
	(1) Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income.
	(2) Income tax reclassifications related to interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income.

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 2015
Asset Retirement Obligation [Abstract]
Changes in AROs	Changes in Questar's AROs from the Condensed Consolidated Balance Sheets were as follows:
		3 Months Ended
		March 31,
		2015			2014
		(in millions)
	AROs at beginning of year	$	69.3		$	67.7
	Accretion	0.8			0.8
	Liabilities incurred	0.1			0.4
	Revisions in estimated cash flows	5.7			0.4
	Liabilities settled	(0.9		)	(0.7		)
	AROs at end of period	$	75		$	68.6

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, by Balance Sheet Grouping	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar's financial statements in this Quarterly Report:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Mar. 31, 2015				Mar. 31, 2014				Dec. 31, 2014
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	4.8	$	4.8	$	5.6	$	5.6	$	32	$	32
	Long-term investment	1	16.2		16.2		15.3		15.3		15.7		15.7
	Financial liabilities
	Short-term debt	1	214		214		157		157		347		347
	Long-term debt, including current portion	2	1,244.80		1,396.30		1,246.60		1,357.50		1,245.20		1,356.10
Questar Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, by Balance Sheet Grouping	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Gas's financial statements in this Quarterly Report:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Mar. 31, 2015				Mar. 31, 2014				Dec. 31, 2014
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	1.4	$	1.4	$	19.8	$	19.8
	Notes receivable from Questar	1	—		—		30.6		30.6		—		—
	Financial liabilities
	Checks outstanding in excess of cash balances	1	0.4		0.4		—		—		—		—
	Notes payable to Questar	1	35.8		35.8		—		—		119.3		119.3
	Long-term debt	2	534.5		629		534.5		588.9		534.5		607.2
Questar Pipeline [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, by Balance Sheet Grouping	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Pipeline's financial statements in this Quarterly Report:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Mar. 31, 2015				Mar. 31, 2014				Dec. 31, 2014
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	6.1	$	6.1	$	4.9	$	4.9	$	7.4	$	7.4
	Notes receivable from Questar	1	35.9		35.9		46.6		46.6		40.1		40.1
	Financial liabilities
	Long-term debt, including current portion	2	458.8		515.1		458.8		509.4		458.8		495.5

Operations_by_Line_of_Business1

Operations by Line of Business (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Summary of operations by line of business	Following is a summary of operations by line of business:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Revenues from Unaffiliated Customers
	Questar Gas	$	374.8		$	396.3		$	939.4		$	963.2
	Wexpro	6.3			12.3			29.6			47.1
	Questar Pipeline	46.8			48			189			189.2
	Other	0.7			0.3			3			0.5
	Total	$	428.6		$	456.9		$	1,161.00		$	1,200.00
	Revenues from Affiliated Companies
	Questar Gas	$	—		$	—		$	—		$	0.3
	Wexpro	84.8			89.1			346			311.1
	Questar Pipeline	19.4			19.3			73.8			76.5
	Total	$	104.2		$	108.4		$	419.8		$	387.9
	Operating Income (Loss)
	Questar Gas	$	76.6		$	69.8		$	116.3		$	107.4
	Wexpro	41.7			48.5			176.5			176.4
	Questar Pipeline	27.4			30.1			114.9			35.4
	Corporate and other	1.3			(0.1		)	(3.6		)	3.5
	Total	$	147		$	148.3		$	404.1		$	322.7
	Net Income (Loss)
	Questar Gas	$	43.8		$	39.6		$	59.4		$	55.4
	Wexpro	27.7			31.8			118.7			116.1
	Questar Pipeline	13.9			15.7			58.8			8.1
	Corporate and other	(0.8		)	(2.0		)	(10.9		)	(6.2		)
	Total	$	84.6		$	85.1		$	226		$	173.4

Employee_Benefits_Tables

Employee Benefits (Tables)	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Schedule of Defined Benefit Plans Disclosures	Components of the qualified and nonqualified net periodic pension cost are listed in the table below:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Service cost	$	3.4		$	3		$	12.2		$	13.4
	Interest cost	8.1			8.4			33.1			31.2
	Expected return on plan assets	(11.6		)	(10.6		)	(44.6		)	(39.2		)
	Prior service cost	—			0.1			0.5			0.9
	Recognized net actuarial loss	5.7			3.9			17.2			26
	Net pension cost	$	5.6		$	4.8		$	18.4		$	32.3
	Net periodic postretirement benefit cost components are listed in the table below:
		3 Months Ended						12 Months Ended
		March 31,						March 31,
		2015			2014			2015			2014
		(in millions)
	Service cost	$	0.2		$	0.2		$	0.6		$	0.7
	Interest cost	0.9			1			3.7			3.7
	Expected return on plan assets	(0.8		)	(0.8		)	(3.0		)	(2.7		)
	Recognized net actuarial loss (gain)	0.3			0.3			0.7			2.6
	Accretion of regulatory liability	0.2			0.2			0.8			0.5
	Net postretirement benefit cost	$	0.8		$	0.9		$	2.8		$	4.8

Nature_of_Business_Details

Nature of Business (Details)	3 Months Ended
	Mar. 31, 2015
	lines_of_business
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of principal complementary lines of business	3

Basis_of_Presentation_of_Inter3

Basis of Presentation of Interim Financial Statements (Details) (USD $)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Cost of Sales [Abstract]
Other cost of sales	$0.30	$0.10	$1.10	$0.20
Total cost of sales	131.8	148.2	169.9	234.4
Questar Gas [Member]
Payments for Questar Gas Acquisition	11.4		11.4
Additional Customers from Questar Gas Acquisition	6,500
Cost of Sales [Abstract]
Gas purchases	41	92.7	84.8	176
Operator service fee	84.8	89.1	345.4	310.9
Transportation and storage	22.2	22.1	79.7	80.2
Gathering	5.4	4.9	21.5	19.1
Royalties	11.9	17.3	54.7	50.5
Storage (injection) withdrawal, net	30.9	33	-3.2	3.4
Purchased-gas account adjustment	36.2	-5.6	-4	-30.3
Other	1.2	1.1	4.9	4.8
Total Questar Gas cost of natural gas sold	233.6	254.6	583.8	614.6
Elimination of Questar Gas cost of natural gas sold - affiliated companies	-104	-108.2	-419.2	-387
Total Questar Gas cost of natural gas sold - unaffiliated parties	129.6	146.4	164.6	227.6
Questar Pipeline [Member]
Ownership percentage in unconsolidated affiliate (in hundredths)	50.00%		50.00%
Cost of Sales [Abstract]
Total Questar Pipeline cost of sales	$1.90	$1.70	$4.20	$6.60

Earnings_Per_Share_Details

Earnings Per Share (Details)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Weighted-average basic common shares outstanding (in shares)	176.2	175.7	176	175.6
Potential number of shares issuable under the Company's LTSIP (in shares)	0.3	0.4	0.3	0.5
Weighted-average diluted common shares outstanding (in shares)	176.5	176.1	176.3	176.1

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Details) (USD $)	3 Months Ended				12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2015		Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period	($201.30)		($141.80)		($139.10)		($241.30)
OCI before reclassifications					-113.6		135.7
Reclassified from AOCI	6.2	[1]	4.5	[1]	18.9	[1]	30	[1]
Income taxes
Attributable to OCI before reclassifications					43.4		-51.8
Attributable to amounts reclassified from AOCI	-2.4	[2]	-1.8	[2]	-7.1	[2]	-11.7	[2]
Total income taxes	2.4		1.8		-36.3		63.5
Net other comprehensive income (loss)	3.8		2.7		-58.4		102.2
AOCI at end of period	-197.5		-139.1		-197.5		-139.1
Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract]
Income tax benefit	-48.8		-50.1		-124.6		-103.5
Pension and OPRB
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period	-178.9		-119		-116.4		-218.3
OCI before reclassifications					-113.6		135.8
Reclassified from AOCI	6	[1]	4.3	[1]	18.4	[1]	29.5	[1]
Income taxes
Attributable to OCI before reclassifications					43.4		-51.9
Attributable to amounts reclassified from AOCI	-2.3	[2]	-1.7	[2]	-7	[2]	-11.5	[2]
Total income taxes					-36.4		63.4
Net other comprehensive income (loss)	3.7		2.6		-58.8		101.9
AOCI at end of period	-175.2		-116.4		-175.2		-116.4
Long-term invest.
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period	0.1		0.1		0.1		0.1
OCI before reclassifications					0		-0.1
Reclassified from AOCI	0	[1]	0	[1]	0	[1]	0	[1]
Income taxes
Attributable to OCI before reclassifications					0		0.1
Attributable to amounts reclassified from AOCI	0	[2]	0	[2]	0	[2]	0	[2]
Total income taxes					0		-0.1
Net other comprehensive income (loss)	0		0		0		0
AOCI at end of period	0.1		0.1		0.1		0.1
Questar Pipeline [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period	-22.5				-22.8
Income taxes
Total income taxes	0.1		0.1		0.1		0.2
Net other comprehensive income (loss)	0.1		0.1		0.4		0.3
AOCI at end of period	-22.4		-22.8		-22.4		-22.8
Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract]
Income tax benefit	-8		-9.1		-34.5		-7
Questar Pipeline [Member] | Interest rate cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period	-22.5		-22.9		-22.8		-23.1
OCI before reclassifications					0		0
Reclassified from AOCI	0.2	[1]	0.2	[1]	0.5	[1]	0.5	[1]
Income taxes
Attributable to OCI before reclassifications					0		0
Attributable to amounts reclassified from AOCI	-0.1	[2]	-0.1	[2]	-0.1	[2]	-0.2	[2]
Total income taxes					0.1		0.2
Net other comprehensive income (loss)	0.1		0.1		0.4		0.3
AOCI at end of period	-22.4		-22.8		-22.4		-22.8
Questar Pipeline [Member] | Interest rate cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract]
Interest (expense)	-0.2		-0.2		-0.5		-0.5
Income tax benefit	$0.10		$0.10		$0.10		$0.20
[1]	Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income.
[2]	Income tax reclassifications related to interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income.

Asset_Retirement_Obligations_D

Asset Retirement Obligations (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at beginning of year	$69.30	$67.70
Accretion	0.8	0.8
Liabilities incurred	0.1	0.4
Revisions in estimated cash flows	5.7	0.4
Liabilities settled	-0.9	-0.7
AROs at end of period	$75	$68.60

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Millions, unless otherwise specified
Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	$4.80	$32	$5.60
Long-term investment	16.2	15.7	15.3
Financial liabilities [Abstract]
Short-term debt	214	347	157
Long-term debt, including current portion	1,244.80	1,245.20	1,246.60
Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	4.8	32	5.6
Financial liabilities [Abstract]
Short-term debt	214	347	157
Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial liabilities [Abstract]
Long-term debt, including current portion	1,396.30	1,356.10	1,357.50
Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Long-term investment	16.2	15.7	15.3
Questar Gas [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	19.8	1.4
Notes receivable from Questar	0	0	30.6
Financial liabilities [Abstract]
Checks outstanding in excess of cash balances	0.4	0	0
Notes payable to Questar	35.8	119.3	0
Long-term debt, including current portion	534.5	534.5	534.5
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	19.8	1.4
Notes receivable from Questar	0	0	30.6
Financial liabilities [Abstract]
Checks outstanding in excess of cash balances	0.4	0	0
Notes payable to Questar	35.8	119.3	0
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial liabilities [Abstract]
Long-term debt, including current portion	629	607.2	588.9
Questar Pipeline [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	6.1	7.4	4.9
Notes receivable from Questar	35.9	40.1	46.6
Financial liabilities [Abstract]
Long-term debt, including current portion	458.8	458.8	458.8
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	6.1	7.4	4.9
Notes receivable from Questar	35.9	40.1	46.6
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial liabilities [Abstract]
Long-term debt, including current portion	$515.10	$495.50	$509.40

Derivatives_and_Hedging_Detail

Derivatives and Hedging (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Dec. 31, 2011	Dec. 31, 2014	Dec. 31, 2011	Mar. 31, 2014
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$0		0		$0
Cash Flow Hedging [Member] | Questar Pipeline [Member] | Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]
Derivative [Line Items]
Notional amount		150,000,000		150,000,000
Debt Instrument, Face Amount		180,000,000		180,000,000
Interest payment for terminated derivative instrument		37,300,000
Life of long-term debt associated with cash flow hedges				30 years
Date Through Which Reclassifications Into Earnings From AOCI Will Take Place			2041
Pre-tax net losses expected to be reclassified from AOCI to Consolidated statement of income	$600,000
Reclassification from accumulated OCI to income, time to transfer	12 months

Operations_by_Line_of_Business2

Operations by Line of Business (Details) (USD $)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
	lines_of_business
Segment Reporting Information [Line Items]
Number of principal complementary lines of business	3
Revenues by Line of Business	$428.60	$456.90	$1,161	$1,200
Operating Income (Loss)	147	148.3	404.1	322.7
Net Income (Loss)	84.6	85.1	226	173.4
Questar Gas [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	374.8	396.3	939.4	963.2
Operating Income (Loss)	76.6	69.8	116.3	107.4
Net Income (Loss)	43.8	39.6	59.4	55.4
Wexpro [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	6.3	12.3	29.6	47.1
Operating Income (Loss)	41.7	48.5	176.5	176.4
Net Income (Loss)	27.7	31.8	118.7	116.1
Questar Pipeline [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	46.8	48	189	189.2
Operating Income (Loss)	27.4	30.1	114.9	35.4
Net Income (Loss)	13.9	15.7	58.8	8.1
Questar Corp and Other [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	0.7	0.3	3	0.5
Operating Income (Loss)	1.3	-0.1	-3.6	3.5
Net Income (Loss)	-0.8	-2	-10.9	-6.2
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	104.2	108.4	419.8	387.9
Intersegment Eliminations [Member] | Questar Gas [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	0	0	0	0.3
Intersegment Eliminations [Member] | Wexpro [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	84.8	89.1	346	311.1
Intersegment Eliminations [Member] | Questar Pipeline [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	$19.40	$19.30	$73.80	$76.50

Employee_Benefits_Details

Employee Benefits (Details) (USD $)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Qualified and nonqualified pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$3.40	$3	$12.20	$13.40
Interest cost	8.1	8.4	33.1	31.2
Expected return on plan assets	-11.6	-10.6	-44.6	-39.2
Prior service cost	0	0.1	0.5	0.9
Recognized net actuarial loss	5.7	3.9	17.2	26
Net benefit cost	5.6	4.8	18.4	32.3
Estimated qualified pension plan cost for current fiscal year	18.9		18.9
Estimated nonqualified pension plan cost for current fiscal year	3.4		3.4
Postretirement benefits plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.2	0.6	0.7
Interest cost	0.9	1	3.7	3.7
Expected return on plan assets	-0.8	-0.8	-3	-2.7
Recognized net actuarial loss (gain)	0.3	0.3	0.7	2.6
Accretion of regulatory liability	0.2	0.2	0.8	0.5
Net benefit cost	0.8	0.9	2.8	4.8
Estimated postretirement benefits cost for current fiscal year, before accretion of regulatory liability	$2.20		$2.20

Contingencies_Details

Contingencies (Details) (USD $)	Mar. 31, 2015
In Millions, unless otherwise specified
Wexpro [Member]
Loss Contingencies [Line Items]
Overriding royalty interest	4.00%
Loss Contingency, Range of Possible Loss, Maximum	$14.10
Unaffiliated Entity [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Maximum	$16.20

Asset_Impairments_Details

Asset Impairments (Details) (USD $)	3 Months Ended		12 Months Ended		3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2014	Sep. 30, 2013
Property, Plant and Equipment [Line Items]
Pre-tax asset impairment charge	$0	$0	$2	$80.60
Wexpro [Member] | Wexpro Brady Field [Member]
Property, Plant and Equipment [Line Items]
Pre-tax asset impairment charge					2
Questar Pipeline [Member]
Property, Plant and Equipment [Line Items]
Pre-tax asset impairment charge	0	0	0	80.6
Questar Pipeline [Member] | Questar Southern Trails Pipeline - Eastern Segment [Member]
Property, Plant and Equipment [Line Items]
Pre-tax asset impairment charge						80.6
After-tax asset impairment charge						$52.40