Questar Pipeline 10-Q 30 Oct 14 2014 Q3 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	9 Months Ended
	Sep. 30, 2014
Entity Information [Line Items]	'
Entity Registrant Name	'QUESTAR CORP
Entity Central Index Key	'0000751652
Current Fiscal Year End Date	'--12-31
Entity Filer Category	'Large Accelerated Filer
Document Type	'10-Q
Document Period End Date	30-Sep-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q3
Amendment Flag	'false
Entity Common Stock, Shares Outstanding	175,256,549
Questar Gas [Member]	'
Entity Information [Line Items]	'
Entity Registrant Name	'QUESTAR GAS CO
Entity Central Index Key	'0000068589
Current Fiscal Year End Date	'--12-31
Entity Filer Category	'Non-accelerated Filer
Document Type	'10-Q
Document Period End Date	30-Sep-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q3
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	'0000764044
Current Fiscal Year End Date	'--12-31
Entity Filer Category	'Non-accelerated Filer
Document Type	'10-Q
Document Period End Date	30-Sep-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q3
Amendment Flag	'false
Entity Common Stock, Shares Outstanding	6,550,843

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
REVENUES	'	'	'	'	'	'
Questar Gas / Revenues from unaffiliated customers	$100.70	$89.40	$642	$647.80	$979.40	$928.80
Wexpro	9.4	13.2	29.5	32	42.6	41
Questar Pipeline / Revenues from unaffiliated customers	47.3	47	143.4	142.3	190.6	195.3
Other	0.5	0	1.2	0	1.4	0
Total Revenues	157.9	149.6	816.1	822.1	1,214	1,165.10
OPERATING EXPENSES	'	'	'	'	'	'
Cost of sales (excluding operating expenses shown separately)	-42.3	-35	81.6	157.4	210.1	250.6
Operating and maintenance	39.2	36.4	136.1	122.2	188.2	169.8
General and administrative	26	24.4	88	90.2	118.8	123
Retirement incentive	0	0	0	0	0	4.9
Production and other taxes	16.8	15.2	53.4	45.2	65.6	55.1
Depreciation, depletion and amortization	50.8	47.4	162.9	143.4	214.3	189.4
Abandonment and impairment	0	80.6	2	80.6	2	80.6
Total Operating Expenses	90.5	169	524	639	799	873.4
Net gain (loss) from asset sales	1.5	0	1.6	0.1	1.3	0.1
OPERATING INCOME (LOSS)	68.9	-19.4	293.7	183.2	416.3	291.8
Interest and other income	2	3.1	5	9.2	5.7	10.5
Income from unconsolidated affiliate	0.9	0.9	2.7	2.8	3.6	3.7
Interest expense	-15.7	-13.9	-47.3	-42.7	-61.5	-56.3
INCOME (LOSS) BEFORE INCOME TAXES	56.1	-29.3	254.1	152.5	364.1	249.7
Income taxes	-17.5	10.1	-90.1	-59.4	-132	-92.8
NET INCOME (LOSS)	38.6	-19.2	164	93.1	232.1	156.9
Earnings (Loss) Per Common Share	'	'	'	'	'	'
Basic	$0.22	($0.11)	$0.93	$0.53	$1.32	$0.89
Diluted	$0.22	($0.11)	$0.93	$0.53	$1.32	$0.89
Weighted-average common shares outstanding	'	'	'	'	'	'
Used in basic calculation	175.8	175.5	175.8	175.4	175.7	175.5
Used in diluted calculation	176.1	175.5	176.1	176.1	176	176.1
Dividends per common share	$0.19	$0.18	$0.56	$0.53	$0.74	$0.70
Questar Gas [Member]	'	'	'	'	'	'
REVENUES	'	'	'	'	'	'
Questar Gas / Revenues from unaffiliated customers	100.7	89.4	642	647.8	979.4	928.8
Revenues from affiliated company	0	0.2	0	0.6	0	0.8
Total Revenues	100.7	89.6	642	648.4	979.4	929.6
OPERATING EXPENSES	'	'	'	'	'	'
Cost of natural gas sold (excluding operating expenses shown separately)	56.8	50.1	398.6	424.2	625	601.1
Operating and maintenance	22.7	20.9	88.8	78.1	123.8	109.9
General and administrative	12.3	12.1	39	38.5	53	53.2
Retirement incentive	0	0	0	0	0	2.4
Depreciation and amortization	13.5	12.4	40.3	36.9	53.1	49.1
Other taxes	4.8	5.3	14.7	15.4	17.3	18.3
Total Operating Expenses	110.1	100.8	581.4	593.1	872.2	834
Net gain (loss) from asset sales	0	0	0.1	0	0.1	0
OPERATING INCOME (LOSS)	-9.4	-11.2	60.7	55.3	107.3	95.6
Interest and other income	1.7	1.3	4.3	3.8	5.6	5.5
Interest expense	-7.1	-5.3	-21.2	-16.7	-26.8	-21.7
INCOME (LOSS) BEFORE INCOME TAXES	-14.8	-15.2	43.8	42.4	86.1	79.4
Income taxes	5.7	6.2	-16.6	-15.6	-32.9	-28.8
NET INCOME (LOSS)	-9.1	-9	27.2	26.8	53.2	50.6
Questar Pipeline [Member]	'	'	'	'	'	'
REVENUES	'	'	'	'	'	'
Questar Pipeline / Revenues from unaffiliated customers	47.3	47	143.4	142.3	190.6	195.3
Revenues from affiliated companies	17.7	17.6	54.7	54.8	76.6	74
Total Revenues	65	64.6	198.1	197.1	267.2	269.3
OPERATING EXPENSES	'	'	'	'	'	'
Operating and maintenance	9.5	8.8	25.5	23.2	34.8	32
General and administrative	10.2	10.8	32.5	35.3	43.9	48.8
Retirement incentive	0	0	0	0	0	0.9
Depreciation and amortization	13.5	14	40.7	42.2	54	55.9
Abandonment and impairment	0	80.6	0	80.6	0	80.6
Other taxes	2.4	2.5	7.1	7.4	9	9.2
Cost of sales (excluding operating expenses shown separately)	0.6	0.5	3	2.7	6.4	7.5
Total Operating Expenses	36.2	117.2	108.8	191.4	148.1	234.9
Net gain (loss) from asset sales	0	0	0	0	0	0.1
OPERATING INCOME (LOSS)	28.8	-52.6	89.3	5.7	119.1	34.5
Interest and other income	0.3	0.6	0.7	1.2	1.3	1.5
Income from unconsolidated affiliate	0.9	0.9	2.7	2.8	3.6	3.7
Interest expense	-6.5	-6.5	-19.6	-19.5	-25.9	-26
INCOME (LOSS) BEFORE INCOME TAXES	23.5	-57.6	73.1	-9.8	98.1	13.7
Income taxes	-8.6	19.7	-26.8	2.2	-36	-6.4
NET INCOME (LOSS)	$14.90	($37.90)	$46.30	($7.60)	$62.10	$7.30

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net income (loss)	$38.60	($19.20)	$164	$93.10	$232.10	$156.90
Other comprehensive income (loss):	'	'	'	'	'	'
Pension and other postretirement benefits	3.7	9	12.5	24.7	156.6	-28.1
Interest rate cash flow hedge amortization	0.1	0.1	0.4	0.4	0.5	0.4
Change in fair value of long-term investment	0	0	0	-0.1	0	-0.1
Income taxes	-1.3	-3.4	-4.9	-9.4	-60.2	10.8
Net other comprehensive income (loss)	2.5	5.7	8	15.6	96.9	-17
COMPREHENSIVE INCOME (LOSS)	41.1	-13.5	172	108.7	329	139.9
Questar Pipeline [Member]	'	'	'	'	'	'
Net income (loss)	14.9	-37.9	46.3	-7.6	62.1	7.3
Other comprehensive income (loss):	'	'	'	'	'	'
Interest rate cash flow hedge amortization	0.1	0.1	0.4	0.4	0.5	0.4
Income taxes	0	0	-0.1	-0.1	-0.2	-0.1
Net other comprehensive income (loss)	0.1	0.1	0.3	0.3	0.3	0.3
COMPREHENSIVE INCOME (LOSS)	$15	($37.80)	$46.60	($7.30)	$62.40	$7.60

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Millions, unless otherwise specified
Current Assets	'	'	'
Cash and cash equivalents	$7.30	$16	$0
Accounts receivable, net	57.3	123.8	58
Unbilled gas accounts receivable	12.8	93.4	11.7
Gas stored underground	69.3	40	59.4
Materials and supplies	25.2	23.7	24
Current regulatory assets	84.2	35.8	49.3
Prepaid expenses and other	6.3	9.5	6
Deferred income taxes - current	14.7	9.7	8.8
Total Current Assets	277.1	351.9	217.2
Property, Plant and Equipment	5,852.30	5,674.70	5,583.80
Accumulated depreciation, depletion and amortization	-2,185.20	-2,071.70	-2,037.90
Net Property, Plant and Equipment	3,667.10	3,603	3,545.90
Investment in unconsolidated affiliate	24.9	25.6	25.8
Noncurrent regulatory assets	18.6	20.5	21.3
Other noncurrent assets	50.2	53.3	50.9
TOTAL ASSETS	4,037.90	4,054.30	3,861.10
Current Liabilities	'	'	'
Checks outstanding in excess of cash balances	0	0	1.6
Short-term debt	234	276	355
Accounts payable and accrued expenses	225.4	264.8	211.6
Current regulatory liabilities	11	14.1	1.8
Current portion of long-term debt and capital lease obligation	1	0.9	0.8
Total Current Liabilities	471.4	555.8	570.8
Long-term debt and capital lease obligation, less current portion	1,283.30	1,285.50	1,136.10
Deferred income taxes	718.5	707.2	645.9
Asset retirement obligations	69.2	67.7	65.9
Defined benefit pension plan and other postretirement benefits	73.3	113.2	257.3
Noncurrent regulatory liabilities	67.9	61.2	59.5
Customer contributions in aid of construction	29.6	29.1	31.5
Other noncurrent liabilities	45.4	35.8	35.5
COMMON SHAREHOLDERS' EQUITY	'	'	'
Common stock	471.5	464.5	449.7
Retained earnings	941.6	876.1	839.6
Accumulated other comprehensive (loss)	-133.8	-141.8	-230.7
Total Common Shareholders' Equity	1,279.30	1,198.80	1,058.60
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	4,037.90	4,054.30	3,861.10
Questar Gas [Member]	'	'	'
Current Assets	'	'	'
Cash and cash equivalents	0	8.8	0
Accounts receivable, net	27.6	88.9	24.2
Unbilled gas accounts receivable	12.8	93.4	11.7
Accounts receivable from affiliates	44.7	30.4	31.4
Gas stored underground	66.8	39.2	56.5
Materials and supplies	14	12.1	12.2
Current regulatory assets	82.6	30.2	45.5
Prepaid expenses and other	2.6	3	2.4
Deferred income taxes - current	3	2.9	1.5
Total Current Assets	254.1	308.9	185.4
Property, Plant and Equipment	2,315.10	2,203	2,147.80
Accumulated depreciation, depletion and amortization	-770.4	-745.2	-739.4
Net Property, Plant and Equipment	1,544.70	1,457.80	1,408.40
Noncurrent regulatory assets	14.4	16.1	16.5
Goodwill	5.6	5.6	5.6
Other noncurrent assets	3.7	4	3
TOTAL ASSETS	1,822.50	1,792.40	1,618.90
Current Liabilities	'	'	'
Checks outstanding in excess of cash balances	2.1	0	1.4
Notes payable to Questar	90.8	17.7	195
Accounts payable and accrued expenses	91.8	139.2	80.3
Accounts payable to affiliates	52.2	67.8	49.9
Customer advances	23.2	19.8	21.9
Current regulatory liabilities	10.4	11.1	0.5
Total Current Liabilities	270.5	255.6	349
Long-term debt and capital lease obligation, less current portion	534.5	534.5	384.5
Deferred income taxes	348.5	340.7	330.7
Noncurrent regulatory liabilities	59.1	53	51.3
Customer contributions in aid of construction	29.6	29.1	31.5
Other noncurrent liabilities	2.8	3.2	3
COMMON SHAREHOLDERS' EQUITY	'	'	'
Common stock	23	23	23
Additional paid-in capital	264.9	263.9	173.6
Retained earnings	289.6	289.4	272.3
Total Common Shareholders' Equity	577.5	576.3	468.9
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	1,822.50	1,792.40	1,618.90
Questar Pipeline [Member]	'	'	'
Current Assets	'	'	'
Cash and cash equivalents	0.4	2.7	1.5
Notes receivable from Questar	35.2	29.4	36.6
Accounts receivable, net	17.3	18.5	17.8
Accounts receivable from affiliates	37.8	36.6	32.7
Gas stored underground	2.5	0.8	2.9
Materials and supplies	6.9	7.3	7.5
Current regulatory assets	1.6	5.6	3.8
Prepaid expenses and other	1.7	4.4	1.8
Deferred income taxes - current	1.8	1.8	1.6
Total Current Assets	105.2	107.1	106.2
Property, Plant and Equipment	1,824	1,774.30	1,766.10
Accumulated depreciation, depletion and amortization	-662.9	-627.2	-617.8
Net Property, Plant and Equipment	1,161.10	1,147.10	1,148.30
Investment in unconsolidated affiliate	24.9	25.6	25.8
Goodwill	4.2	4.2	4.2
Noncurrent regulatory and other assets	7.2	7.7	8.2
TOTAL ASSETS	1,302.60	1,291.70	1,292.70
Current Liabilities	'	'	'
Accounts payable and accrued expenses	41.1	25.6	35.9
Accounts payable to affiliates	3.6	9.4	3.7
Current regulatory liabilities	0.6	3	1.3
Total Current Liabilities	45.3	38	40.9
Long-term debt and capital lease obligation, less current portion	458.8	458.9	458.8
Deferred income taxes	230	228.6	226.9
Noncurrent regulatory and other liabilities	16.1	13.9	13.9
COMMON SHAREHOLDERS' EQUITY	'	'	'
Common stock	6.6	6.6	6.6
Additional paid-in capital	351	349.5	349.2
Retained earnings	217.4	219.1	219.3
Accumulated other comprehensive (loss)	-22.6	-22.9	-22.9
Total Common Shareholders' Equity	552.4	552.3	552.2
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	$1,302.60	$1,291.70	$1,292.70

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
OPERATING ACTIVITIES	'	'
Net income (loss)	$164	$93.10
Adjustments to reconcile net income (loss) to net cash provided by operating activities:	'	'
Depreciation, depletion and amortization	169.1	148.7
Deferred income taxes	1.4	37.2
Abandonment and impairment	2	80.6
Share-based compensation	8.5	7.7
Net (gain) loss from asset sales	-1.6	-0.1
(Income) from unconsolidated affiliate	-2.7	-2.8
Distributions from unconsolidated affiliate and other	4.1	4.2
Changes in operating assets and liabilities	17.7	55.4
Net Cash Provided By Operating Activities	362.5	424
INVESTING ACTIVITIES	'	'
Property, plant and equipment	-235.3	-287.4
Wexpro acquisition of producing properties	0	-106.7
Cash used in disposition of assets	-2.6	-3.1
Proceeds from disposition of assets	9.4	0.6
Net Cash Used In Investing Activities	-228.5	-396.6
FINANCING ACTIVITIES	'	'
Common stock issued	1	2.2
Common stock repurchased	-3.8	-4.2
Change in short-term debt	-42	92
Checks outstanding in excess of cash balances	0	1.6
Long-term debt and capital lease obligation repaid	-0.7	-42.6
Long-term debt issuance costs	0	-1.7
Dividends paid	-98.5	-93
Tax benefits from share-based compensation	1.3	1.5
Net Cash Provided By (Used In) Financing Activities	-142.7	-44.2
Change in cash and cash equivalents	-8.7	-16.8
Beginning cash and cash equivalents	16	16.8
Ending cash and cash equivalents	7.3	0
Questar Gas [Member]	'	'
OPERATING ACTIVITIES	'	'
Net income (loss)	27.2	26.8
Adjustments to reconcile net income (loss) to net cash provided by operating activities:	'	'
Depreciation and amortization	44.2	40.7
Deferred income taxes	7.7	29.1
Share-based compensation	1	1.1
Net (gain) loss from asset sales	-0.1	0
Changes in operating assets and liabilities	2.6	49.9
Net Cash Provided By Operating Activities	82.6	147.6
INVESTING ACTIVITIES	'	'
Property, plant and equipment	-138.2	-119.3
Cash used in disposition of assets	-2.2	-2.5
Proceeds from disposition of assets	0.8	0.3
Affiliated-company property, plant and equipment transfers	0	10.8
Net Cash Used In Investing Activities	-139.6	-110.7
FINANCING ACTIVITIES	'	'
Change in notes payable to Questar	73.1	28.9
Checks outstanding in excess of cash balances	2.1	1.4
Long-term debt and capital lease obligation repaid	0	-42
Dividends paid to Questar	-27	-26.6
Net Cash Provided By (Used In) Financing Activities	48.2	-38.3
Change in cash and cash equivalents	-8.8	-1.4
Beginning cash and cash equivalents	8.8	1.4
Ending cash and cash equivalents	0	0
Questar Pipeline [Member]	'	'
OPERATING ACTIVITIES	'	'
Net income (loss)	46.3	-7.6
Adjustments to reconcile net income (loss) to net cash provided by operating activities:	'	'
Depreciation and amortization	42.5	44.1
Deferred income taxes	1.3	-15.7
Abandonment and impairment	0	80.6
Share-based compensation	1.5	1.6
(Income) from unconsolidated affiliate	-2.7	-2.8
Distributions from unconsolidated affiliate and other	3.8	3.9
Changes in operating assets and liabilities	4.3	3.6
Net Cash Provided By Operating Activities	97	107.7
INVESTING ACTIVITIES	'	'
Property, plant and equipment	-45.3	-56.2
Cash used in disposition of assets	-0.4	-0.6
Proceeds from disposition of assets	0.2	0.1
Affiliated-company property, plant and equipment transfers	0	-10.7
Net Cash Used In Investing Activities	-45.5	-67.4
FINANCING ACTIVITIES	'	'
Change in notes receivable from Questar	-5.8	2.1
Dividends paid to Questar	-48	-48
Net Cash Provided By (Used In) Financing Activities	-53.8	-45.9
Change in cash and cash equivalents	-2.3	-5.6
Beginning cash and cash equivalents	2.7	7.1
Ending cash and cash equivalents	$0.40	$1.50

Nature_of_Business_Notes

Nature of Business (Notes)	9 Months Ended
	Sep. 30, 2014
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)	9 Months Ended
	Sep. 30, 2014
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, 2013.
	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, nine and 12 months ended September 30, 2014, are not necessarily indicative of the results that may be expected for the year ending December 31, 2014.
	Certain reclassifications were made to prior year information to conform to the current year presentation. Questar and Questar Gas reclassified amounts received from customers for the cost of plant removal from accumulated depreciation to a regulatory liability for the prior year. These reclassifications did not impact net income or cash flows. The Company does not believe these changes are material to prior year financial statements.
	Questar uses the equity method to account for its investment in an unconsolidated affiliate where it does not have control, but has significant influence. White River Hub, LLC is a limited liability company and FERC-regulated transporter of natural gas. Questar Pipeline owns 50% of White River Hub, LLC and is the operator. Generally, the investment in White River Hub, LLC on the Company's balance sheets equals the Company's proportionate share of equity reported by White River Hub, LLC. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below the Company'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.
	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. 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						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Questar Gas
	Gas purchases	$	0.1		$	0.1		$	96.7		$	113.7		$	169.6		$	153.6
	Operator service fee	82.3			68.2			265.8			215.2			345.2			284.7
	Transportation and storage	18.1			18.5			58.8			58.6			80.3			79.7
	Gathering	4.5			4.5			14.2			13.6			19.4			18.1
	Royalties	14.9			11			50.5			32.4			62.4			41
	Storage (injection) withdrawal, net	(39.0		)	(37.3		)	(27.6		)	(18.1		)	(10.3		)	1.9
	Purchased-gas account adjustment	(25.3		)	(15.9		)	(63.4		)	5.1			(46.5		)	17.2
	Other	1.2			1			3.6			3.7			4.9			4.9
	Total Questar Gas cost of natural gas sold	56.8			50.1			398.6			424.2			625			601.1
	Elimination of Questar Gas cost of natural gas sold - affiliated companies	(99.9		)	(85.6		)	(320.6		)	(269.5		)	(422.0		)	(358.0		)
	Total Questar Gas cost of natural gas sold - unaffiliated parties	(43.1		)	(35.5		)	78			154.7			203			243.1
	Questar Pipeline
	Total Questar Pipeline cost of sales	0.6			0.5			3			2.7			6.4			7.5
	Other cost of sales	0.2			—			0.6			—			0.7			—
	Total cost of sales	$	(42.3	)	$	(35.0	)	$	81.6		$	157.4		$	210.1		$	250.6

Earnings_Per_Share_Notes

Earnings Per Share (Notes)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	Note 3 - Earnings (Loss) Per Share
	Basic earnings (loss) per share (EPS) is computed by dividing net income (loss) 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 dividends 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 are participating securities for the computation of basic EPS. The application of the two-class method had an insignificant impact on the calculation of both basic and diluted EPS. A reconciliation of the components of basic and diluted shares used in the EPS calculation follows:
		3 Months Ended		9 Months Ended		12 Months Ended
		September 30,		September 30,		September 30,
		2014	2013	2014	2013	2014	2013
		(in millions)
	Weighted-average basic common shares outstanding	175.8	175.5	175.8	175.4	175.7	175.5
	Potential number of shares issuable under the Company's LTSIP	0.3	—	0.3	0.7	0.3	0.6
	Weighted-average diluted common shares outstanding	176.1	175.5	176.1	176.1	176	176.1
	There were no potential shares included in the diluted EPS calculation for the third quarter of 2013 because any such shares would be anti-dilutive due to the net loss in the quarter.

Other_Comprehensive_Income_Not

Other Comprehensive Income (Notes)	9 Months Ended
	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]	'
Other Comprehensive Income	'
	Note 4 - Other Comprehensive Income
	Comprehensive income (loss), as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income (loss) 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 (OPRB) costs are accrued, as the Company records interest expense for hedged interest payments and when the long-term investment is sold or otherwise realized.
	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 OPRB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPRB			Interest rate cash flow hedges			Long-term invest.			Total
		3 Months Ended											3 Months Ended
		September 30, 2014											September 30, 2013
		(in millions)
	AOCI at beginning of period	$	(113.7	)	$	(22.7	)	$	0.1	$	(136.3	)	$	(213.5	)	$	(23.0	)	$	0.1		$	(236.4	)
	Reclassified from AOCI(1)	3.7			0.1			—		3.8			9			0.1			—			9.1
	Income taxes
	Reclassified from AOCI(2)	(1.3		)	—			—		(1.3		)	(3.4		)	—			—			(3.4		)
	Net other comprehensive income	2.4			0.1			—		2.5			5.6			0.1			—			5.7
	AOCI at September 30,	$	(111.3	)	$	(22.6	)	$	0.1	$	(133.8	)	$	(207.9	)	$	(22.9	)	$	0.1		$	(230.7	)
		Pension and OPRB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPRB			Interest rate cash flow hedges			Long-term invest.			Total
		9 Months Ended											9 Months Ended
		September 30, 2014											September 30, 2013
		(in millions)
	AOCI at beginning of period	$	(119.0	)	$	(22.9	)	$	0.1	$	(141.8	)	$	(223.2	)	$	(23.2	)	$	0.1		$	(246.3	)
	OCI before reclassifications	—			—			—		—			—			—			(0.1		)	(0.1		)
	Reclassified from AOCI(1)	12.5			0.4			—		12.9			24.7			0.4			—			25.1
	Income taxes
	OCI before reclassifications	—			—			—		—			—			—			0.1			0.1
	Reclassified from AOCI(2)	(4.8		)	(0.1		)	—		(4.9		)	(9.4		)	(0.1		)	—			(9.5		)
	Total income taxes	(4.8		)	(0.1		)	—		(4.9		)	(9.4		)	(0.1		)	0.1			(9.4		)
	Net other comprehensive income	7.7			0.3			—		8			15.3			0.3			—			15.6
	AOCI at September 30,	$	(111.3	)	$	(22.6	)	$	0.1	$	(133.8	)	$	(207.9	)	$	(22.9	)	$	0.1		$	(230.7	)
		Pension and OPRB			Interest rate cash flow hedges			Long-term invest.		Total
		12 Months Ended
		September 30, 2014
		(in millions)
	AOCI at beginning of period	$	(207.9	)	$	(22.9	)	$	0.1	$	(230.7	)
	OCI before reclassifications	135.8			—			—		135.8
	Reclassified from AOCI(1)	20.8			0.5			—		21.3
	Income taxes
	OCI before reclassifications	(51.9		)	—			—		(51.9		)
	Reclassified from AOCI(2)	(8.1		)	(0.2		)	—		(8.3		)
	Total income taxes	(60.0		)	(0.2		)	—		(60.2		)
	Net other comprehensive income	96.6			0.3			—		96.9
	AOCI at September 30,	$	(111.3	)	$	(22.6	)	$	0.1	$	(133.8	)
	(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 10 for additional details.
	Comprehensive income (loss), as reported in Questar Pipeline's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income (loss) 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)	9 Months Ended
	Sep. 30, 2014
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:
		9 Months Ended
		September 30,
		2014			2013
		(in millions)
	AROs at beginning of year	$	67.7		$	67.2
	Accretion	2.5			2.4
	Liabilities incurred	0.7			4.2
	Revisions in estimated cash flows	0.4			(6.8		)
	Liabilities settled	(2.1		)	(1.1		)
	AROs at September 30,	$	69.2		$	65.9
	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 Agreement and Wexpro II Agreement 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)	9 Months Ended
	Sep. 30, 2014
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. Fair value accounting standards also apply to certain nonfinancial assets and liabilities that are measured at fair value on a nonrecurring basis.
	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 on Form 10-Q:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Sept. 30, 2014				Sept. 30, 2013				Dec. 31, 2013
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	7.3	$	7.3	$	—	$	—	$	16	$	16
	Long-term investment	1	15.8		15.8		16.8		16.8		17.3		17.3
	Financial liabilities
	Checks outstanding in excess of cash balances	1	—		—		1.6		1.6		—		—
	Short-term debt	1	234		234		355		355		276		276
	Long-term debt	2	1,245.70		1,364.00		1,097.50		1,191.10		1,247.10		1,310.80
	The carrying amounts of cash and cash equivalents, checks outstanding in excess of cash balances and short-term debt approximate fair value. 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 on Form 10-Q:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Sept. 30, 2014				Sept. 30, 2013				Dec. 31, 2013
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	—	$	—	$	8.8	$	8.8
	Financial liabilities
	Checks outstanding in excess of cash balances	1	2.1		2.1		1.4		1.4		—		—
	Notes payable to Questar	1	90.8		90.8		195		195		17.7		17.7
	Long-term debt	2	534.5		602.8		384.5		425.6		534.5		568
	The carrying amounts of cash and cash equivalents and checks outstanding in excess of cash balances approximate fair value. The carrying amounts of 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 on Form 10-Q:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Sept. 30, 2014				Sept. 30, 2013				Dec. 31, 2013
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	0.4	$	0.4	$	1.5	$	1.5	$	2.7	$	2.7
	Notes receivable from Questar	1	35.2		35.2		36.6		36.6		29.4		29.4
	Financial liabilities
	Long-term debt	2	458.8		505		458.8		505.5		458.9		486
	The carrying amounts of cash and cash equivalents approximate fair value. 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.
	The Questar and Questar Pipeline Condensed Consolidated Balance Sheets included a nonrecurring fair value measurement at September 30, 2013 related to the impairment of the eastern segment of Questar Southern Trails Pipeline. The asset's fair value of zero was based on inputs that indicated overall negative future net cash flows. 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. Based on this analysis, Questar Pipeline determined that the asset was impaired. This is a Level 3 fair value measurement because the inputs are unobservable. See Note 12 for additional information.

Derivatives_and_Hedging_Notes

Derivatives and Hedging (Notes)	9 Months Ended
	Sep. 30, 2014
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, nine and 12 months ended September 30, 2014 and September 30, 2013.
	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 September 30, 2014, 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 September 30, 2014, September 30, 2013 or December 31, 2013.

ShareBased_Compensation_Notes

Share-Based Compensation (Notes)	9 Months Ended
	Sep. 30, 2014
Share-based Compensation [Abstract]	'
Share-Based Compensation	'
	Note 8 - Share-Based Compensation
	Questar may issue stock options, restricted shares, RSUs and performance shares to certain of its officers, employees and non-employee directors under the LTSIP. Questar recognizes expense over time as the stock options, restricted shares, RSUs and performance shares vest. Total share-based compensation expense amounted to $8.5 million for the first nine months of 2014 compared to $7.7 million in 2013. Deferred share-based compensation, representing the unvested value of restricted share and RSU awards, amounted to $6.8 million at September 30, 2014. Cash flow from income tax benefits in excess of recognized compensation expense amounted to $1.3 million for the first nine months of 2014 compared to $1.5 million for the same period in 2013. There were 4,041,007 shares available for future grants at September 30, 2014.
	Stock Options
	There were no unvested stock options at September 30, 2014. No stock options were granted or forfeited in the first nine months of 2014. Stock option transactions and balances under the terms of the LTSIP are summarized below:
		Options			Exercise						Weighted-Average Exercise Price
		Outstanding			Price Range
	Balance at December 31, 2013	717,840			$	7.84	-	$	17.35		$	11.84
	Exercised	(67,559	)		7.84		-	13.1			8.78
	Balance at September 30, 2014	650,281			$	7.84	-	$	17.35		$	12.16
	Options Outstanding													Options Exercisable
	Range of exercise prices							Number outstanding at Sept. 30, 2014		Weighted-average remaining term in years		Weighted-average exercise price		Number exercisable at Sept. 30, 2014	Weighted-average exercise price
	$	7.84		-	$	11.4		341,948		1.3		$	10.9	341,948	$	10.9
	13.1			-	17.35			308,333		1.8		13.55		308,333	13.55
								650,281		1.5		$	12.16	650,281	$	12.16
	Certain officers, employees and non-employee directors of former subsidiary QEP Resources held 245,332 Questar stock options with a weighted-average exercise price of $11.34 per share and a weighted-average remaining life of 1.7 years at September 30, 2014.
	Restricted Shares
	Restricted share grants typically vest in equal installments over a three-year period from the grant date. Several grants vest in a single installment after a specified period. The weighted-average remaining vesting period of unvested restricted shares at September 30, 2014, was 5 months. No restricted shares were granted in the first nine months of 2014.
	Transactions involving restricted shares under the terms of the LTSIP are summarized below:
		Restricted			Price Range						Weighted-Average Price
		Shares
		Outstanding
	Balance at December 31, 2013	392,327			$	15.22	-	$	21.53		$	18.28
	Vested	(284,154	)		15.22		-	21.53			17.85
	Forfeited	(661	)		19.39		-	20.9			20
	Balance at September 30, 2014	107,512			$	15.98	-	$	21.53		$	19.41
	Restricted Stock Units
	Questar may grant RSUs to certain of its officers, employees and non-employee directors under the LTSIP. One share of Questar common stock will be distributed for each RSU at the time of vesting. RSU grants typically vest in equal installments over a three-year period from the grant date. Several grants vest in a single installment after a specified period. The weighted-average remaining vesting period of unvested RSUs at September 30, 2014, was 15 months. Transactions involving RSUs under the terms of the LTSIP are summarized below:
		RSUs			Price Range						Weighted-Average Price
		Outstanding
	Balance at December 31, 2013	316,268			$	22.17	-	$	25.44		$	23.62
	Granted	353,540			22.81		-	24.7			23.6
	Vested	(131,007	)		22.17		-	25.44			23.64
	Forfeited	(10,225	)		23.6		-	23.62			23.6
	Balance at September 30, 2014	528,576			$	22.17	-	$	24.7		$	23.6
	Questar may grant RSUs with deferred share distributions (deferred RSUs) to certain of its non-employee directors under the LTSIP. Grants of deferred RSUs typically vest in a single installment over a one-year period from the grant date. At September 30, 2014, Questar's outstanding deferred RSUs totaled 17,355 with a weighted-average price of $23.60 per share. The weighted-average remaining vesting period of unvested deferred RSUs at September 30, 2014, was 5 months. One share of Questar common stock will be distributed for each vested deferred RSU (including accrued reinvested dividend equivalents) at the time of the grantees' separation from service.
	Performance Shares
	Questar may grant performance shares to certain of its officers under the terms of the LTSIP. The awards are designed to motivate and reward these officers for long-term Company performance and provide an incentive for them to remain with the Company. The target number of performance shares for each officer is subject to adjustment upward or downward based on the Company's total shareholder return relative to a specified peer group of companies over a three-year performance period. Each three-year performance period commences at the beginning of the year of grant. Distributions of performance shares, if any, take place in the quarter following the conclusion of the performance period, so long as such officer was employed by the Company or its affiliates as of the last day of the performance period.
	For performance shares granted in 2012 and 2013, half of any award will be distributed in shares of Questar common stock and half in cash. Thereafter, any award will be distributed in shares, with no cash component. For share-settled performance share awards, the grant-date fair value of the awards is amortized to expense over the vesting period. The Monte Carlo simulation method is used to estimate the grant-date fair value of the performance share awards. The liability associated with awards to be settled in cash is adjusted to its estimated fair value through earnings on a quarterly basis. Equity- and liability-based performance share compensation expense amounted to $2.0 million in the first nine months of 2014 and $1.2 million in the first nine months of 2013. The weighted-average remaining vesting period of unvested performance shares at September 30, 2014, was 15 months.
	Performance share transactions under the terms of the LTSIP are summarized below:
		Target Number of Performance Shares Outstanding			Grant-Date						Weighted- Average Grant-Date Fair Value
					Fair Value Range
	Balance at December 31, 2013	387,879			$	18.23	-	$	39.62		$	27.61
	Granted	139,611			31.07			31.07			31.07
	Payout adjustment(1)	(76,657	)		18.23			18.23			18.23
	Distributed(1)	(51,104	)		18.23			18.23			18.23
	Forfeited	(5,660	)		25.42		-	39.62			33.06
	Balance at September 30, 2014	394,069			$	25.42	-	$	39.62		$	31.8
	(1) Actual shares and cash distributed were determined by multiplying the target shares by 0.40 to reflect Questar's final total shareholder return ranking relative to the specified peer companies for the performance period from January 1, 2011 through December 31, 2013.
	The above September 30, 2014 balance includes 6,475 vested target performance shares with a weighted-average grant-date fair value of $30.08 and expected distribution dates ranging from the first quarter of 2015 through the first quarter of 2017.

Operations_by_Line_of_Business

Operations by Line of Business (Notes)	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Operations by Line of Business	'
	Note 9 - 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. 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						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Revenues from Unaffiliated Customers
	Questar Gas	$	100.7		$	89.4		$	642		$	647.8		$	979.4		$	928.8
	Wexpro	9.4			13.2			29.5			32			42.6			41
	Questar Pipeline	47.3			47			143.4			142.3			190.6			195.3
	Other	0.5			—			1.2			—			1.4			—
	Total	$	157.9		$	149.6		$	816.1		$	822.1		$	1,214.00		$	1,165.10
	Revenues from Affiliated Companies
	Questar Gas	$	—		$	0.2		$	—		$	0.6		$	—		$	0.8
	Wexpro	82.3			68.1			266.3			215.2			345.9			284.7
	Questar Pipeline	17.7			17.6			54.7			54.8			76.6			74
	Total	$	100		$	85.9		$	321		$	270.6		$	422.5		$	359.5
	Operating Income (Loss)
	Questar Gas	$	(9.4	)	$	(11.2	)	$	60.7		$	55.3		$	107.3		$	95.6
	Wexpro	47.2			40.7			141.5			121.9			187.3			162.1
	Questar Pipeline	28.8			(52.6		)	89.3			5.7			119.1			34.5
	Corporate and other	2.3			3.7			2.2			0.3			2.6			(0.4		)
	Total	$	68.9		$	(19.4	)	$	293.7		$	183.2		$	416.3		$	291.8
	Net Income (Loss)
	Questar Gas	$	(9.1	)	$	(9.0	)	$	27.2		$	26.8		$	53.2		$	50.6
	Wexpro	31.1			27.5			93			82.2			121.4			109.6
	Questar Pipeline	14.9			(37.9		)	46.3			(7.6		)	62.1			7.3
	Corporate and other	1.7			0.2			(2.5		)	(8.3		)	(4.6		)	(10.6		)
	Total	$	38.6		$	(19.2	)	$	164		$	93.1		$	232.1		$	156.9

Employee_Benefits_Notes

Employee Benefits (Notes)	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Employee Benefits	'
	Note 10 - 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 2014 estimated net cost for the qualified pension plan is $13.6 million. The projected 2014 qualified pension plan funding is $43.0 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; claims are paid from the Company's general funds. The 2014 estimated net cost for the nonqualified pension plan is $4.0 million.
	Components of the qualified and nonqualified net periodic pension cost are listed in the table below:
		3 Months Ended						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Service cost	$	2.9		$	3.3		$	8.9		$	10.4		$	12.4		$	13.4
	Interest cost	8.3			7.5			25			23			32.6			31.3
	Expected return on plan assets	(11.4		)	(9.5		)	(32.7		)	(28.6		)	(42.2		)	(36.7		)
	Prior service and other costs	0.1			0.2			0.4			0.8			0.7			0.8
	Recognized net actuarial loss	3.7			8			11.6			21.7			18.8			30.4
	Net pension cost	$	3.6		$	9.5		$	13.2		$	27.3		$	22.3		$	39.2
	The Company currently estimates a $2.1 million net cost for postretirement benefits other than pensions in 2014, before accretion of a regulatory liability. Net periodic postretirement benefit cost components are listed in the table below:
		3 Months Ended						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Service cost	$	0.2		$	0.2		$	0.5		$	0.6		$	0.6		$	0.8
	Interest cost	0.9			0.9			2.9			2.8			3.8			3.8
	Expected return on plan assets	(0.8		)	(0.6		)	(2.3		)	(1.9		)	(3.0		)	(2.5		)
	Amortization of transition obligation	—			—			—			—			—			0.4
	Recognized net actuarial loss (gain)	(0.1		)	0.8			0.5			2.2			1.3			3.1
	Accretion of regulatory liability	0.2			0.2			0.6			0.5			0.6			0.3
	Net postretirement benefit cost	$	0.4		$	1.5		$	2.2		$	4.2		$	3.3		$	5.9

Contingencies_Notes

Contingencies (Notes)	9 Months Ended
	Sep. 30, 2014
Contingencies [Abstract]	'
Contingencies	'
	Note 11 - Contingencies
	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 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 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 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. Amended pleadings have been filed naming Wexpro Company as an additional plaintiff and counterclaim defendant and the following parties as successors in interest to QEP Field Services as defendants and counterclaimants: 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. While Questar Gas and Wexpro intend to vigorously pursue their 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 an adverse material effect on their financial position, results of operations or cash flows.
	Questar incurs environmental remediation costs related to both owned and previously-owned facilities, including transmission and production facilities, manufactured gas plant sites and a previously-owned chemical business.
	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 above concerning the QEP lawsuit, management does not believe any of them 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.

Asset_Impairments_Notes

Asset Impairments (Notes)	9 Months Ended
	Sep. 30, 2014
Strategic Review of Questar Southern Trails Pipeline and Impairment of Eastern Segment [Abstract]	'
Asset Impairments	'
	Note 12 - 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.

Wexpro_Acquisition_of_Producin

Wexpro Acquisition of Producing Properties and Inclusion in Wexpro II Agreement (Notes)	9 Months Ended
	Sep. 30, 2014
Wexpro Acquisition of Producing Properties [Abstract]	'
Wexpro Acquisition of Producing Properties and Inclusion in Wexpro II Agreement	'
	Note 13 - Wexpro Acquisition of Producing Properties and Inclusion in Wexpro II Agreement
	On September 4, 2013, Wexpro completed the transaction announced in July 2013 to acquire an additional interest in natural gas-producing properties in the Trail Unit of southwestern Wyoming's Vermillion Basin (Trail acquisition). This acquisition was an addition to the company’s existing Trail assets, which are governed by the 1981 Wexpro Agreement. In the first quarter of 2014, the Public Service Commission of Utah and the Wyoming Public Service Commission (the Commissions) approved the inclusion of these properties in the Wexpro II Agreement, effective February 1, 2014. The Wexpro II Agreement is modeled after the terms of the original Wexpro Agreement. Under the Wexpro II Agreement, Wexpro may acquire gas development properties and Questar Gas may submit an application to the Commissions to treat these properties similar to the original Wexpro properties. If the Commissions approve the applications, the gas will be developed for the benefit of Questar Gas customers. Wexpro will be entitled to a return on the acquisition costs based on Questar Gas's approved cost of capital. Future development investment will earn returns consistent with the original Wexpro Agreement.

Recent_Accounting_Developments

Recent Accounting Developments (Notes)	9 Months Ended
	Sep. 30, 2014
Recent Accounting Developments [Abstract]	'
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]	'
	Note 14 - Recent Accounting Developments
	In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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 and cash flows, as well as which transition approach it will take.

Basis_of_Presentation_of_Inter1

Basis of Presentation of Interim Financial Statements (Policies)	9 Months Ended
	Sep. 30, 2014
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 uses the equity method to account for its investment in an unconsolidated affiliate where it does not have control, but has significant influence. White River Hub, LLC is a limited liability company and FERC-regulated transporter of natural gas. Questar Pipeline owns 50% of White River Hub, LLC and is the operator. Generally, the investment in White River Hub, LLC on the Company's balance sheets equals the Company's proportionate share of equity reported by White River Hub, LLC. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below the Company'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.
Earnings Per Share	'
	Basic earnings (loss) per share (EPS) is computed by dividing net income (loss) 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 dividends 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 are participating securities for the computation of basic EPS. The application of the two-class method had an insignificant impact on the calculation of both basic and diluted EPS.
Comprehensive Income - Questar	'
	Comprehensive income (loss), as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income (loss) 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 (OPRB) costs are accrued, as the Company records interest expense for hedged interest payments and when the long-term investment is sold or otherwise realized.
Comprehensive Income - Questar Pipeline	'
	Comprehensive income (loss), as reported in Questar Pipeline's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income (loss) 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.

Basis_of_Presentation_of_Inter2

Basis of Presentation of Interim Financial Statements (Tables)	9 Months Ended
	Sep. 30, 2014
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						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Questar Gas
	Gas purchases	$	0.1		$	0.1		$	96.7		$	113.7		$	169.6		$	153.6
	Operator service fee	82.3			68.2			265.8			215.2			345.2			284.7
	Transportation and storage	18.1			18.5			58.8			58.6			80.3			79.7
	Gathering	4.5			4.5			14.2			13.6			19.4			18.1
	Royalties	14.9			11			50.5			32.4			62.4			41
	Storage (injection) withdrawal, net	(39.0		)	(37.3		)	(27.6		)	(18.1		)	(10.3		)	1.9
	Purchased-gas account adjustment	(25.3		)	(15.9		)	(63.4		)	5.1			(46.5		)	17.2
	Other	1.2			1			3.6			3.7			4.9			4.9
	Total Questar Gas cost of natural gas sold	56.8			50.1			398.6			424.2			625			601.1
	Elimination of Questar Gas cost of natural gas sold - affiliated companies	(99.9		)	(85.6		)	(320.6		)	(269.5		)	(422.0		)	(358.0		)
	Total Questar Gas cost of natural gas sold - unaffiliated parties	(43.1		)	(35.5		)	78			154.7			203			243.1
	Questar Pipeline
	Total Questar Pipeline cost of sales	0.6			0.5			3			2.7			6.4			7.5
	Other cost of sales	0.2			—			0.6			—			0.7			—
	Total cost of sales	$	(42.3	)	$	(35.0	)	$	81.6		$	157.4		$	210.1		$	250.6

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2014
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		9 Months Ended		12 Months Ended
		September 30,		September 30,		September 30,
		2014	2013	2014	2013	2014	2013
		(in millions)
	Weighted-average basic common shares outstanding	175.8	175.5	175.8	175.4	175.7	175.5
	Potential number of shares issuable under the Company's LTSIP	0.3	—	0.3	0.7	0.3	0.6
	Weighted-average diluted common shares outstanding	176.1	175.5	176.1	176.1	176	176.1

Other_Comprehensive_Income_Tab

Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2014
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 OPRB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPRB			Interest rate cash flow hedges			Long-term invest.			Total
		3 Months Ended											3 Months Ended
		September 30, 2014											September 30, 2013
		(in millions)
	AOCI at beginning of period	$	(113.7	)	$	(22.7	)	$	0.1	$	(136.3	)	$	(213.5	)	$	(23.0	)	$	0.1		$	(236.4	)
	Reclassified from AOCI(1)	3.7			0.1			—		3.8			9			0.1			—			9.1
	Income taxes
	Reclassified from AOCI(2)	(1.3		)	—			—		(1.3		)	(3.4		)	—			—			(3.4		)
	Net other comprehensive income	2.4			0.1			—		2.5			5.6			0.1			—			5.7
	AOCI at September 30,	$	(111.3	)	$	(22.6	)	$	0.1	$	(133.8	)	$	(207.9	)	$	(22.9	)	$	0.1		$	(230.7	)
		Pension and OPRB			Interest rate cash flow hedges			Long-term invest.		Total			Pension and OPRB			Interest rate cash flow hedges			Long-term invest.			Total
		9 Months Ended											9 Months Ended
		September 30, 2014											September 30, 2013
		(in millions)
	AOCI at beginning of period	$	(119.0	)	$	(22.9	)	$	0.1	$	(141.8	)	$	(223.2	)	$	(23.2	)	$	0.1		$	(246.3	)
	OCI before reclassifications	—			—			—		—			—			—			(0.1		)	(0.1		)
	Reclassified from AOCI(1)	12.5			0.4			—		12.9			24.7			0.4			—			25.1
	Income taxes
	OCI before reclassifications	—			—			—		—			—			—			0.1			0.1
	Reclassified from AOCI(2)	(4.8		)	(0.1		)	—		(4.9		)	(9.4		)	(0.1		)	—			(9.5		)
	Total income taxes	(4.8		)	(0.1		)	—		(4.9		)	(9.4		)	(0.1		)	0.1			(9.4		)
	Net other comprehensive income	7.7			0.3			—		8			15.3			0.3			—			15.6
	AOCI at September 30,	$	(111.3	)	$	(22.6	)	$	0.1	$	(133.8	)	$	(207.9	)	$	(22.9	)	$	0.1		$	(230.7	)
		Pension and OPRB			Interest rate cash flow hedges			Long-term invest.		Total
		12 Months Ended
		September 30, 2014
		(in millions)
	AOCI at beginning of period	$	(207.9	)	$	(22.9	)	$	0.1	$	(230.7	)
	OCI before reclassifications	135.8			—			—		135.8
	Reclassified from AOCI(1)	20.8			0.5			—		21.3
	Income taxes
	OCI before reclassifications	(51.9		)	—			—		(51.9		)
	Reclassified from AOCI(2)	(8.1		)	(0.2		)	—		(8.3		)
	Total income taxes	(60.0		)	(0.2		)	—		(60.2		)
	Net other comprehensive income	96.6			0.3			—		96.9
	AOCI at September 30,	$	(111.3	)	$	(22.6	)	$	0.1	$	(133.8	)
	(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)	9 Months Ended
	Sep. 30, 2014
Asset Retirement Obligation [Abstract]	'
Changes in AROs	'
	Changes in Questar's AROs from the Condensed Consolidated Balance Sheets were as follows:
		9 Months Ended
		September 30,
		2014			2013
		(in millions)
	AROs at beginning of year	$	67.7		$	67.2
	Accretion	2.5			2.4
	Liabilities incurred	0.7			4.2
	Revisions in estimated cash flows	0.4			(6.8		)
	Liabilities settled	(2.1		)	(1.1		)
	AROs at September 30,	$	69.2		$	65.9

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
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 on Form 10-Q:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Sept. 30, 2014				Sept. 30, 2013				Dec. 31, 2013
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	7.3	$	7.3	$	—	$	—	$	16	$	16
	Long-term investment	1	15.8		15.8		16.8		16.8		17.3		17.3
	Financial liabilities
	Checks outstanding in excess of cash balances	1	—		—		1.6		1.6		—		—
	Short-term debt	1	234		234		355		355		276		276
	Long-term debt	2	1,245.70		1,364.00		1,097.50		1,191.10		1,247.10		1,310.80
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 on Form 10-Q:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Sept. 30, 2014				Sept. 30, 2013				Dec. 31, 2013
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	—	$	—	$	8.8	$	8.8
	Financial liabilities
	Checks outstanding in excess of cash balances	1	2.1		2.1		1.4		1.4		—		—
	Notes payable to Questar	1	90.8		90.8		195		195		17.7		17.7
	Long-term debt	2	534.5		602.8		384.5		425.6		534.5		568
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 on Form 10-Q:
		Hierarchy Level of Fair Value Estimates	Carrying		Estimated		Carrying		Estimated		Carrying		Estimated
			Amount		Fair Value		Amount		Fair Value		Amount		Fair Value
			Sept. 30, 2014				Sept. 30, 2013				Dec. 31, 2013
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	0.4	$	0.4	$	1.5	$	1.5	$	2.7	$	2.7
	Notes receivable from Questar	1	35.2		35.2		36.6		36.6		29.4		29.4
	Financial liabilities
	Long-term debt	2	458.8		505		458.8		505.5		458.9		486

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2014
Share-based Compensation [Abstract]	'
Transactions involving stock options under the terms of the LTSIP	'
	Stock option transactions and balances under the terms of the LTSIP are summarized below:
		Options			Exercise						Weighted-Average Exercise Price
		Outstanding			Price Range
	Balance at December 31, 2013	717,840			$	7.84	-	$	17.35		$	11.84
	Exercised	(67,559	)		7.84		-	13.1			8.78
	Balance at September 30, 2014	650,281			$	7.84	-	$	17.35		$	12.16
Options held under the LTSIP, by exercise price range	'
	Options Outstanding													Options Exercisable
	Range of exercise prices							Number outstanding at Sept. 30, 2014		Weighted-average remaining term in years		Weighted-average exercise price		Number exercisable at Sept. 30, 2014	Weighted-average exercise price
	$	7.84		-	$	11.4		341,948		1.3		$	10.9	341,948	$	10.9
	13.1			-	17.35			308,333		1.8		13.55		308,333	13.55
								650,281		1.5		$	12.16	650,281	$	12.16
Transactions involving restricted shares and RSUs under the terms of the LTSIP	'
	Transactions involving restricted shares under the terms of the LTSIP are summarized below:
		Restricted			Price Range						Weighted-Average Price
		Shares
		Outstanding
	Balance at December 31, 2013	392,327			$	15.22	-	$	21.53		$	18.28
	Vested	(284,154	)		15.22		-	21.53			17.85
	Forfeited	(661	)		19.39		-	20.9			20
	Balance at September 30, 2014	107,512			$	15.98	-	$	21.53		$	19.41
	Transactions involving RSUs under the terms of the LTSIP are summarized below:
		RSUs			Price Range						Weighted-Average Price
		Outstanding
	Balance at December 31, 2013	316,268			$	22.17	-	$	25.44		$	23.62
	Granted	353,540			22.81		-	24.7			23.6
	Vested	(131,007	)		22.17		-	25.44			23.64
	Forfeited	(10,225	)		23.6		-	23.62			23.6
	Balance at September 30, 2014	528,576			$	22.17	-	$	24.7		$	23.6
Transactions involving performance shares under the terms of the LTSIP	'
	Performance share transactions under the terms of the LTSIP are summarized below:
		Target Number of Performance Shares Outstanding			Grant-Date						Weighted- Average Grant-Date Fair Value
					Fair Value Range
	Balance at December 31, 2013	387,879			$	18.23	-	$	39.62		$	27.61
	Granted	139,611			31.07			31.07			31.07
	Payout adjustment(1)	(76,657	)		18.23			18.23			18.23
	Distributed(1)	(51,104	)		18.23			18.23			18.23
	Forfeited	(5,660	)		25.42		-	39.62			33.06
	Balance at September 30, 2014	394,069			$	25.42	-	$	39.62		$	31.8
	(1) Actual shares and cash distributed were determined by multiplying the target shares by 0.40 to reflect Questar's final total shareholder return ranking relative to the specified peer companies for the performance period from January 1, 2011 through December 31, 2013.

Operations_by_Line_of_Business1

Operations by Line of Business (Tables)	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Summary of operations by line of business	'
	Following is a summary of operations by line of business:
		3 Months Ended						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Revenues from Unaffiliated Customers
	Questar Gas	$	100.7		$	89.4		$	642		$	647.8		$	979.4		$	928.8
	Wexpro	9.4			13.2			29.5			32			42.6			41
	Questar Pipeline	47.3			47			143.4			142.3			190.6			195.3
	Other	0.5			—			1.2			—			1.4			—
	Total	$	157.9		$	149.6		$	816.1		$	822.1		$	1,214.00		$	1,165.10
	Revenues from Affiliated Companies
	Questar Gas	$	—		$	0.2		$	—		$	0.6		$	—		$	0.8
	Wexpro	82.3			68.1			266.3			215.2			345.9			284.7
	Questar Pipeline	17.7			17.6			54.7			54.8			76.6			74
	Total	$	100		$	85.9		$	321		$	270.6		$	422.5		$	359.5
	Operating Income (Loss)
	Questar Gas	$	(9.4	)	$	(11.2	)	$	60.7		$	55.3		$	107.3		$	95.6
	Wexpro	47.2			40.7			141.5			121.9			187.3			162.1
	Questar Pipeline	28.8			(52.6		)	89.3			5.7			119.1			34.5
	Corporate and other	2.3			3.7			2.2			0.3			2.6			(0.4		)
	Total	$	68.9		$	(19.4	)	$	293.7		$	183.2		$	416.3		$	291.8
	Net Income (Loss)
	Questar Gas	$	(9.1	)	$	(9.0	)	$	27.2		$	26.8		$	53.2		$	50.6
	Wexpro	31.1			27.5			93			82.2			121.4			109.6
	Questar Pipeline	14.9			(37.9		)	46.3			(7.6		)	62.1			7.3
	Corporate and other	1.7			0.2			(2.5		)	(8.3		)	(4.6		)	(10.6		)
	Total	$	38.6		$	(19.2	)	$	164		$	93.1		$	232.1		$	156.9

Employee_Benefits_Tables

Employee Benefits (Tables)	9 Months Ended
	Sep. 30, 2014
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						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Service cost	$	2.9		$	3.3		$	8.9		$	10.4		$	12.4		$	13.4
	Interest cost	8.3			7.5			25			23			32.6			31.3
	Expected return on plan assets	(11.4		)	(9.5		)	(32.7		)	(28.6		)	(42.2		)	(36.7		)
	Prior service and other costs	0.1			0.2			0.4			0.8			0.7			0.8
	Recognized net actuarial loss	3.7			8			11.6			21.7			18.8			30.4
	Net pension cost	$	3.6		$	9.5		$	13.2		$	27.3		$	22.3		$	39.2
	Net periodic postretirement benefit cost components are listed in the table below:
		3 Months Ended						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2014			2013			2014			2013			2014			2013
		(in millions)
	Service cost	$	0.2		$	0.2		$	0.5		$	0.6		$	0.6		$	0.8
	Interest cost	0.9			0.9			2.9			2.8			3.8			3.8
	Expected return on plan assets	(0.8		)	(0.6		)	(2.3		)	(1.9		)	(3.0		)	(2.5		)
	Amortization of transition obligation	—			—			—			—			—			0.4
	Recognized net actuarial loss (gain)	(0.1		)	0.8			0.5			2.2			1.3			3.1
	Accretion of regulatory liability	0.2			0.2			0.6			0.5			0.6			0.3
	Net postretirement benefit cost	$	0.4		$	1.5		$	2.2		$	4.2		$	3.3		$	5.9

Nature_of_Business_Details

Nature of Business (Details)	9 Months Ended
	Sep. 30, 2014
	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		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'	'	'	'	'	'
Ownership percentage in unconsolidated affiliate (in hundredths)	50.00%	'	50.00%	'	50.00%	'
Cost of Sales [Abstract]	'	'	'	'	'	'
Other cost of sales	$0.20	$0	$0.60	$0	$0.70	$0
Total cost of sales	-42.3	-35	81.6	157.4	210.1	250.6
Questar Gas [Member]	'	'	'	'	'	'
Cost of Sales [Abstract]	'	'	'	'	'	'
Gas purchases	0.1	0.1	96.7	113.7	169.6	153.6
Operator service fee	82.3	68.2	265.8	215.2	345.2	284.7
Transportation and storage	18.1	18.5	58.8	58.6	80.3	79.7
Gathering	4.5	4.5	14.2	13.6	19.4	18.1
Royalties	14.9	11	50.5	32.4	62.4	41
Storage (injection) withdrawal, net	-39	-37.3	-27.6	-18.1	-10.3	1.9
Purchased-gas account adjustment	-25.3	-15.9	-63.4	5.1	-46.5	17.2
Other	1.2	1	3.6	3.7	4.9	4.9
Total Questar Gas cost of natural gas sold	56.8	50.1	398.6	424.2	625	601.1
Elimination of Questar Gas cost of natural gas sold - affiliated companies	-99.9	-85.6	-320.6	-269.5	-422	-358
Total Questar Gas cost of natural gas sold - unaffiliated parties	-43.1	-35.5	78	154.7	203	243.1
Questar Pipeline [Member]	'	'	'	'	'	'
Cost of Sales [Abstract]	'	'	'	'	'	'
Total Questar Pipeline cost of sales	$0.60	$0.50	$3	$2.70	$6.40	$7.50

Earnings_Per_Share_Details

Earnings Per Share (Details)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]	'	'	'	'	'	'
Weighted-average basic common shares outstanding (in shares)	175.8	175.5	175.8	175.4	175.7	175.5
Potential number of shares issuable under the Company's LTSIP (in shares)	0.3	0	0.3	0.7	0.3	0.6
Weighted-average diluted common shares outstanding (in shares)	176.1	175.5	176.1	176.1	176	176.1

Other_Comprehensive_Income_Det

Other Comprehensive Income (Details) (USD $)	3 Months Ended				9 Months Ended				12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'		'		'		'		'
AOCI at beginning of period	($136.30)		($236.40)		($141.80)		($246.30)		($230.70)		'
OCI before reclassifications	'		'		0		-0.1		135.8		'
Reclassified from AOCI	3.8	[1]	9.1	[1]	12.9	[1]	25.1	[1]	21.3	[1]	'
Income taxes	'		'		'		'		'		'
Attributable to OCI before reclassifications	'		'		0		0.1		-51.9		'
Attributable to amounts reclassified from AOCI	-1.3	[2]	-3.4	[2]	-4.9	[2]	-9.5	[2]	-8.3	[2]	'
Total income taxes	-1.3		-3.4		-4.9		-9.4		-60.2		10.8
Net other comprehensive income (loss)	2.5		5.7		8		15.6		96.9		-17
AOCI at September 30,	-133.8		-230.7		-133.8		-230.7		-133.8		-230.7
Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract]	'		'		'		'		'		'
Income tax benefit	-17.5		10.1		-90.1		-59.4		-132		-92.8
Pension and OPRB	'		'		'		'		'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'		'		'		'		'
AOCI at beginning of period	-113.7		-213.5		-119		-223.2		-207.9		'
OCI before reclassifications	'		'		0		0		135.8		'
Reclassified from AOCI	3.7	[1]	9	[1]	12.5	[1]	24.7	[1]	20.8	[1]	'
Income taxes	'		'		'		'		'		'
Attributable to OCI before reclassifications	'		'		0		0		-51.9		'
Attributable to amounts reclassified from AOCI	-1.3	[2]	-3.4	[2]	-4.8	[2]	-9.4	[2]	-8.1	[2]	'
Total income taxes	'		'		-4.8		-9.4		-60		'
Net other comprehensive income (loss)	2.4		5.6		7.7		15.3		96.6		'
AOCI at September 30,	-111.3		-207.9		-111.3		-207.9		-111.3		-207.9
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		0.1		'
OCI before reclassifications	'		'		0		-0.1		0		'
Reclassified from AOCI	0	[1]	0	[1]	0	[1]	0	[1]	0	[1]	'
Income taxes	'		'		'		'		'		'
Attributable to OCI before reclassifications	'		'		0		0.1		0		'
Attributable to amounts reclassified from AOCI	0	[2]	0	[2]	0	[2]	0	[2]	0	[2]	'
Total income taxes	'		'		0		0.1		0		'
Net other comprehensive income (loss)	0		0		0		0		0		'
AOCI at September 30,	0.1		0.1		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	'		'		-22.9		'		-22.9		'
Income taxes	'		'		'		'		'		'
Total income taxes	0		0		-0.1		-0.1		-0.2		-0.1
Net other comprehensive income (loss)	0.1		0.1		0.3		0.3		0.3		0.3
AOCI at September 30,	-22.6		-22.9		-22.6		-22.9		-22.6		-22.9
Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract]	'		'		'		'		'		'
Income tax benefit	-8.6		19.7		-26.8		2.2		-36		-6.4
Questar Pipeline [Member] | Interest rate cash flow hedges	'		'		'		'		'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'		'		'		'		'
AOCI at beginning of period	-22.7		-23		-22.9		-23.2		-22.9		'
OCI before reclassifications	'		'		0		0		0		'
Reclassified from AOCI	0.1	[1]	0.1	[1]	0.4	[1]	0.4	[1]	0.5	[1]	'
Income taxes	'		'		'		'		'		'
Attributable to OCI before reclassifications	'		'		0		0		0		'
Attributable to amounts reclassified from AOCI	0	[2]	0	[2]	-0.1	[2]	-0.1	[2]	-0.2	[2]	'
Total income taxes	'		'		-0.1		-0.1		-0.2		'
Net other comprehensive income (loss)	0.1		0.1		0.3		0.3		0.3		'
AOCI at September 30,	-22.6		-22.9		-22.6		-22.9		-22.6		-22.9
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)	-0.1		-0.1		-0.4		-0.4		-0.5		'
Income tax benefit	$0		$0		$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 $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
AROs at beginning of year	$67.70	$67.20
Accretion	2.5	2.4
Liabilities incurred	0.7	4.2
Revisions in estimated cash flows	0.4	-6.8
Liabilities settled	-2.1	-1.1
AROs at September 30,	$69.20	$65.90

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Carrying Amount [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	$7,300,000	$16,000,000	$0
Long-term investment	15,800,000	17,300,000	16,800,000
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	0	0	1,600,000
Short-term debt	234,000,000	276,000,000	355,000,000
Long-term debt	1,245,700,000	1,247,100,000	1,097,500,000
Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	7,300,000	16,000,000	0
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	0	0	1,600,000
Short-term debt	234,000,000	276,000,000	355,000,000
Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]	'	'	'
Financial liabilities [Abstract]	'	'	'
Long-term debt	1,364,000,000	1,310,800,000	1,191,100,000
Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Long-term investment	15,800,000	17,300,000	16,800,000
Questar Gas [Member] | Carrying Amount [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	0	8,800,000	0
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	2,100,000	0	1,400,000
Notes payable to Questar	90,800,000	17,700,000	195,000,000
Long-term debt	534,500,000	534,500,000	384,500,000
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	0	8,800,000	0
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	2,100,000	0	1,400,000
Notes payable to Questar	90,800,000	17,700,000	195,000,000
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]	'	'	'
Financial liabilities [Abstract]	'	'	'
Long-term debt	602,800,000	568,000,000	425,600,000
Questar Pipeline [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]	'	'	'
Financial liabilities [Abstract]	'	'	'
Property, Plant, and Equipment, Fair Value Disclosure	'	'	0
Questar Pipeline [Member] | Carrying Amount [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	400,000	2,700,000	1,500,000
Notes receivable from Questar	35,200,000	29,400,000	36,600,000
Financial liabilities [Abstract]	'	'	'
Long-term debt	458,800,000	458,900,000	458,800,000
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	400,000	2,700,000	1,500,000
Notes receivable from Questar	35,200,000	29,400,000	36,600,000
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]	'	'	'
Financial liabilities [Abstract]	'	'	'
Long-term debt	$505,000,000	$486,000,000	$505,500,000

Derivatives_and_Hedging_Detail

Derivatives and Hedging (Details) (Cash Flow Hedging [Member], Questar Pipeline [Member], Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member], USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2011
Cash Flow Hedging [Member] | Questar Pipeline [Member] | Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]	'	'
Derivative [Line Items]	'	'
Notional amount	'	$150
Debt Instrument, Face Amount	'	180
Interest payment for terminated derivative instrument	'	37.3
Life of long-term debt associated with cash flow hedges	'	'30 years
Pre-tax net losses expected to be reclassified from AOCI to Consolidated statement of income	$0.60	'
Reclassification from accumulated OCI to income, time to transfer	'12 months	'

ShareBased_Compensation_Genera

Share-Based Compensation General (Details) (USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation [Abstract]	'	'
Share-based compensation	$8.50	$7.70
Deferred share-based compensation on restricted share awards and restricted stock unit awards	6.8	'
Cash flow from income tax benefits in excess of recognized compensation expense	$1.30	$1.50
Shares available for future grant (in shares)	4,041,007	'

ShareBased_Compensation_Stock_

Share-Based Compensation Stock options (Details) (Stock Options [Member], USD $)	9 Months Ended
	Sep. 30, 2014
Stock option transactions under the terms of the LTSIP - shares [Roll Forward]	'
Balance at December 31, 2013	717,840
Granted	0
Exercised	-67,559
Forfeited	0
Balance at September 30, 2014	650,281
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at December 31, 2013	$11.84
Exercised	$8.78
Balance at September 30, 2014	$12.16
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]	'
Options Outstanding, Number outstanding at end of period (in shares)	650,281
Options Outstanding, Weighted-average remaining term (in years and months)	'1 year 6 months
Options Outstanding, Weighted-average exercise price	$12.16
Options Exercisable, Number exercisable at end of period	650,281
Options Exercisable, Weighted-average exercise price	$12.16
Stock options, additional disclosures [Abstract]	'
Number of unvested options at end of period (in shares)	0
Number of Questar stock options held by certain officers, employees and nonemployee directors of QEP (in shares)	245,332
Weighted-average exercise price of Questar stock options awarded to certain officers, employees and nonemployee directors of QEP (in dollars per share)	$11.34
Weighted-average remaining life of Questar stock options held by certain officers, employees and nonemployee directors of QEP (in years)	'1 year 8 months
$7.84 - $11.40 [Member]	'
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]	'
Range of exercise prices, lower limit	$7.84
Range of exercise prices, upper limit	$11.40
Options Outstanding, Number outstanding at end of period (in shares)	341,948
Options Outstanding, Weighted-average remaining term (in years and months)	'1 year 3 months
Options Outstanding, Weighted-average exercise price	$10.90
Options Exercisable, Number exercisable at end of period	341,948
Options Exercisable, Weighted-average exercise price	$10.90
$13.10 - $17.35 [Member]	'
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]	'
Range of exercise prices, lower limit	$13.10
Range of exercise prices, upper limit	$17.35
Options Outstanding, Number outstanding at end of period (in shares)	308,333
Options Outstanding, Weighted-average remaining term (in years and months)	'1 year 9 months
Options Outstanding, Weighted-average exercise price	$13.55
Options Exercisable, Number exercisable at end of period	308,333
Options Exercisable, Weighted-average exercise price	$13.55
Minimum [Member]	'
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at December 31, 2013	$7.84
Exercised	$7.84
Balance at September 30, 2014	$7.84
Maximum [Member]	'
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at December 31, 2013	$17.35
Exercised	$13.10
Balance at September 30, 2014	$17.35

ShareBased_Compensation_Restri

Share-Based Compensation Restricted shares (Details) (Restricted Shares [Member], USD $)	9 Months Ended
	Sep. 30, 2014
Transactions under the terms of the LTSIP - shares [Roll Forward]	'
Balance at December 31, 2013	392,327
Granted	0
Vested	-284,154
Forfeited	-661
Balance at September 30, 2014	107,512
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2013	$18.28
Vested	$17.85
Forfeited	$20
Balance at September 30, 2014	$19.41
Share-based awards other than options, additional disclosures [Abstract]	'
Vesting period for share-based award (in years)	'3 years
Weighted-average remaining vesting period of share-based awards (in months)	'5 months
Minimum [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2013	$15.22
Vested	$15.22
Forfeited	$19.39
Balance at September 30, 2014	$15.98
Maximum [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2013	$21.53
Vested	$21.53
Forfeited	$20.90
Balance at September 30, 2014	$21.53

ShareBased_Compensation_Restri1

Share-Based Compensation Restricted stock units (Details) (USD $)	9 Months Ended
	Sep. 30, 2014
Restricted Stock Units (RSUs) [Member]	'
Transactions under the terms of the LTSIP - shares [Roll Forward]	'
Balance at December 31, 2013	316,268
Granted	353,540
Vested	-131,007
Forfeited	-10,225
Balance at September 30, 2014	528,576
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2013	$23.62
Granted	$23.60
Vested	$23.64
Forfeited	$23.60
Balance at September 30, 2014	$23.60
Share-based awards other than options, additional disclosures [Abstract]	'
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Vesting period for share-based award (in years)	'3 years
Weighted-average remaining vesting period of share-based awards (in months)	'15 months
Weighted-average price of deferred restricted stock units outstanding	$23.60
Restricted Stock Units (RSUs) [Member] | Minimum [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2013	$22.17
Granted	$22.81
Vested	$22.17
Forfeited	$23.60
Balance at September 30, 2014	$22.17
Share-based awards other than options, additional disclosures [Abstract]	'
Weighted-average price of deferred restricted stock units outstanding	$22.17
Restricted Stock Units (RSUs) [Member] | Maximum [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2013	$25.44
Granted	$24.70
Vested	$25.44
Forfeited	$23.62
Balance at September 30, 2014	$24.70
Share-based awards other than options, additional disclosures [Abstract]	'
Weighted-average price of deferred restricted stock units outstanding	$24.70
Deferred Restricted Stock Units (RSUs) [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at September 30, 2014	$23.60
Share-based awards other than options, additional disclosures [Abstract]	'
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Vesting period for share-based award (in years)	'1 year
Weighted-average remaining vesting period of share-based awards (in months)	'5 months
Number of deferred restricted stock units outstanding (in shares)	17,355
Weighted-average price of deferred restricted stock units outstanding	$23.60

ShareBased_Compensation_Perfor

Share-Based Compensation Performance shares (Details) (USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Share-based awards other than options, additional disclosures [Abstract]	'		'
Equity- and liability-based performance share compensation expense	$8.50		$7.70
Performance Shares [Member]	'		'
Transactions under the terms of the LTSIP - shares [Roll Forward]	'		'
Balance at December 31, 2013	387,879		'
Granted	139,611		'
Payout adjustment	-76,657	[1]	'
Distributed	-51,104	[1]	'
Forfeited	-5,660		'
Balance at September 30, 2014	394,069		'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'		'
Balance at December 31, 2013	$27.61		'
Granted	$31.07		'
Payout adjustment	$18.23	[1]	'
Distributed	$18.23	[1]	'
Forfeited	$33.06		'
Balance at September 30, 2014	$31.80		'
Share-based awards other than options, additional disclosures [Abstract]	'		'
Performance period that the target number of performance shares for each exectutive officer is subject to adjustment based on the company's performance (in years)	'3 years		'
Equity- and liability-based performance share compensation expense	$2		$1.20
Weighted-average remaining vesting period of share-based awards (in months)	'15 months		'
Performance share payout adjustment factor (in hundredths)	0.4		'
Weighted-average grant-date fair value of vested undistributed performance shares outstanding	$31.80		'
Performance Shares [Member] | Vested Undistributed [Member]	'		'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'		'
Balance at September 30, 2014	$30.08		'
Share-based awards other than options, additional disclosures [Abstract]	'		'
Number of vested undistributed performance shares outstanding (in shares)	6,475		'
Weighted-average grant-date fair value of vested undistributed performance shares outstanding	$30.08		'
Performance Shares [Member] | Minimum [Member]	'		'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'		'
Balance at December 31, 2013	$18.23		'
Granted	$31.07		'
Payout adjustment	$18.23	[1]	'
Distributed	$18.23	[1]	'
Forfeited	$25.42		'
Balance at September 30, 2014	$25.42		'
Share-based awards other than options, additional disclosures [Abstract]	'		'
Weighted-average grant-date fair value of vested undistributed performance shares outstanding	$25.42		'
Performance Shares [Member] | Minimum [Member] | Vested Undistributed [Member]	'		'
Share-based awards other than options, additional disclosures [Abstract]	'		'
The date the actual performance shares (if any) will be distributed	'first quarter of 2015		'
Performance Shares [Member] | Maximum [Member]	'		'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'		'
Balance at December 31, 2013	$39.62		'
Granted	$31.07		'
Payout adjustment	$18.23	[1]	'
Distributed	$18.23	[1]	'
Forfeited	$39.62		'
Balance at September 30, 2014	$39.62		'
Share-based awards other than options, additional disclosures [Abstract]	'		'
Weighted-average grant-date fair value of vested undistributed performance shares outstanding	$39.62		'
Performance Shares [Member] | Maximum [Member] | Vested Undistributed [Member]	'		'
Share-based awards other than options, additional disclosures [Abstract]	'		'
The date the actual performance shares (if any) will be distributed	'first quarter of 2017		'
[1]	Actual shares and cash distributed were determined by multiplying the target shares by 0.40 to reflect Questar's final total shareholder return ranking relative to the specified peer companies for the performance period from January 1, 2011 through December 31, 2013.

Operations_by_Line_of_Business2

Operations by Line of Business (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
			lines_of_business
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Number of principal complementary lines of business	'	'	3	'	'	'
Revenues by Line of Business	$157.90	$149.60	$816.10	$822.10	$1,214	$1,165.10
Operating Income (Loss)	68.9	-19.4	293.7	183.2	416.3	291.8
Net Income (Loss)	38.6	-19.2	164	93.1	232.1	156.9
Questar Gas [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	100.7	89.4	642	647.8	979.4	928.8
Operating Income (Loss)	-9.4	-11.2	60.7	55.3	107.3	95.6
Net Income (Loss)	-9.1	-9	27.2	26.8	53.2	50.6
Wexpro [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	9.4	13.2	29.5	32	42.6	41
Operating Income (Loss)	47.2	40.7	141.5	121.9	187.3	162.1
Net Income (Loss)	31.1	27.5	93	82.2	121.4	109.6
Questar Pipeline [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	47.3	47	143.4	142.3	190.6	195.3
Operating Income (Loss)	28.8	-52.6	89.3	5.7	119.1	34.5
Net Income (Loss)	14.9	-37.9	46.3	-7.6	62.1	7.3
Questar Corp and Other [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	0.5	0	1.2	0	1.4	0
Operating Income (Loss)	2.3	3.7	2.2	0.3	2.6	-0.4
Net Income (Loss)	1.7	0.2	-2.5	-8.3	-4.6	-10.6
Intersegment Eliminations [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	100	85.9	321	270.6	422.5	359.5
Intersegment Eliminations [Member] | Questar Gas [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	0	0.2	0	0.6	0	0.8
Intersegment Eliminations [Member] | Wexpro [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	82.3	68.1	266.3	215.2	345.9	284.7
Intersegment Eliminations [Member] | Questar Pipeline [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues by Line of Business	$17.70	$17.60	$54.70	$54.80	$76.60	$74

Employee_Benefits_Details

Employee Benefits (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Qualified and nonqualified pension plans [Member]	'	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'	'
Service cost	$2.90	$3.30	$8.90	$10.40	$12.40	$13.40
Interest cost	8.3	7.5	25	23	32.6	31.3
Expected return on plan assets	-11.4	-9.5	-32.7	-28.6	-42.2	-36.7
Prior service and other costs	0.1	0.2	0.4	0.8	0.7	0.8
Recognized net actuarial loss	3.7	8	11.6	21.7	18.8	30.4
Net benefit cost	3.6	9.5	13.2	27.3	22.3	39.2
Estimated qualified pension plan cost for current fiscal year	13.6	'	13.6	'	13.6	'
Projected current year qualified pension plan funding	'	'	43	'	'	'
Estimated nonqualified pension plan cost for current fiscal year	4	'	4	'	4	'
Postretirement benefits plan [Member]	'	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'	'
Service cost	0.2	0.2	0.5	0.6	0.6	0.8
Interest cost	0.9	0.9	2.9	2.8	3.8	3.8
Expected return on plan assets	-0.8	-0.6	-2.3	-1.9	-3	-2.5
Amortization of transition obligation	0	0	0	0	0	0.4
Recognized net actuarial loss (gain)	-0.1	0.8	0.5	2.2	1.3	3.1
Accretion of regulatory liability	0.2	0.2	0.6	0.5	0.6	0.3
Net benefit cost	0.4	1.5	2.2	4.2	3.3	5.9
Estimated postretirement benefits cost for current fiscal year, before accretion of regulatory liability	$2.10	'	$2.10	'	$2.10	'

Asset_Impairments_Details

Asset Impairments (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Property, Plant and Equipment [Line Items]	'	'	'	'	'	'
Pre-tax asset impairment charge	$0	$80.60	$2	$80.60	$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	80.6	0	80.6	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	'	'	'	'

Wexpro_Acquisition_of_Producin1

Wexpro Acquisition of Producing Properties and Inclusion in Wexpro II Agreement (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2014
Business Acquisition [Line Items]	'	'
Business Acquisition, Effective Date of Acquisition	4-Sep-13	'
Business Acquisition, Date of Acquisition Agreement	25-Jul-13	'
Business Acquisition, Description of Acquired Entity	'an additional interest in natural gas-producing properties in the Trail Unit of southwestern Wyoming's Vermillion Basin	'
Date of Acquisition's Inclusion under Wexpro II Agreement	'	1-Feb-14