Questar Gas 10-Q 31 Oct 13 2013 Q3 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	9 Months Ended
	Sep. 30, 2013
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-13
Document Fiscal Year Focus	'2013
Document Fiscal Period Focus	'Q3
Amendment Flag	'false
Entity Common Stock, Shares Outstanding	175,070,395
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-13
Document Fiscal Year Focus	'2013
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-13
Document Fiscal Year Focus	'2013
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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
REVENUES	'	'	'	'	'	'
Questar Gas / Revenues from unaffiliated customers	$89.40	$82.50	$647.80	$578.70	$928.80	$876.50
Wexpro	13.2	9.8	32	27.1	41	35.5
Questar Pipeline / Revenues from unaffiliated customers	47	49.5	142.3	150.1	195.3	198.7
Total Revenues	149.6	141.8	822.1	755.9	1,165.10	1,110.70
OPERATING EXPENSES	'	'	'	'	'	'
Cost of sales (excluding operating expenses shown separately)	-35	-42.1	157.4	99.1	250.6	209.5
Operating and maintenance	36.4	36.8	122.2	133.2	169.8	182.5
General and administrative	24.4	29	90.2	88	123	122.6
Retirement incentive	0	0	0	0	4.9	0
Production and other taxes	15.2	11.1	45.2	38	55.1	50.3
Depreciation, depletion and amortization	47.4	45.9	143.4	135.6	189.4	177.1
Asset impairment	80.6	0	80.6	0	80.6	0
Total Operating Expenses	169	80.7	639	493.9	873.4	742
Net gain (loss) from asset sales	0	2.5	0.1	5.1	0.1	5
OPERATING INCOME (LOSS)	-19.4	63.6	183.2	267.1	291.8	373.7
Interest and other income	3.1	1.7	9.2	5.7	10.5	7.2
Income from unconsolidated affiliate	0.9	1	2.8	2.8	3.7	3.7
Interest expense	-13.9	-14.5	-42.7	-44.3	-56.3	-57
INCOME (LOSS) BEFORE INCOME TAXES	-29.3	51.8	152.5	231.3	249.7	327.6
Income taxes	10.1	-18	-59.4	-83.1	-92.8	-117.8
NET INCOME (LOSS)	-19.2	33.8	93.1	148.2	156.9	209.8
Earnings (Loss) Per Common Share	'	'	'	'	'	'
Basic	($0.11)	$0.20	$0.53	$0.84	$0.89	$1.18
Diluted	($0.11)	$0.19	$0.53	$0.83	$0.89	$1.18
Weighted-average common shares outstanding	'	'	'	'	'	'
Used in basic calculation	175.5	175.4	175.4	177	175.5	177.2
Used in diluted calculation	175.5	176.5	176.1	178.1	176.1	178.3
Dividends per common share (in dollars per share)	$0.18	$0.17	$0.53	$0.50	$0.70	$0.66
Questar Gas [Member]	'	'	'	'	'	'
REVENUES	'	'	'	'	'	'
Questar Gas / Revenues from unaffiliated customers	89.4	82.5	647.8	578.7	928.8	876.5
Revenues from affiliated company	0.2	0.5	0.6	2.3	0.8	3.4
Total Revenues	89.6	83	648.4	581	929.6	879.9
OPERATING EXPENSES	'	'	'	'	'	'
Cost of natural gas sold (excluding operating expenses shown separately)	50.1	44.7	424.2	356.4	601.1	551.6
Operating and maintenance	20.9	21.4	78.1	87.2	109.9	123.1
General and administrative	12.1	12.1	38.5	36.5	53.2	52.6
Retirement incentive	0	0	0	0	2.4	0
Depreciation and amortization	12.4	11.4	36.9	35	49.1	46.6
Other taxes	5.3	4.1	15.4	13.3	18.3	15.9
Total Operating Expenses	100.8	93.7	593.1	528.4	834	789.8
OPERATING INCOME (LOSS)	-11.2	-10.7	55.3	52.6	95.6	90.1
Interest and other income	1.3	1.4	3.8	3.8	5.5	4.9
Interest expense	-5.3	-5.8	-16.7	-19.1	-21.7	-25.5
INCOME (LOSS) BEFORE INCOME TAXES	-15.2	-15.1	42.4	37.3	79.4	69.5
Income taxes	6.2	5.8	-15.6	-14	-28.8	-26
NET INCOME (LOSS)	-9	-9.3	26.8	23.3	50.6	43.5
Questar Pipeline [Member]	'	'	'	'	'	'
REVENUES	'	'	'	'	'	'
Questar Pipeline / Revenues from unaffiliated customers	47	49.5	142.3	150.1	195.3	198.7
Revenues from affiliated companies	17.6	18.4	54.8	55.2	74	73.8
Total Revenues	64.6	67.9	197.1	205.3	269.3	272.5
OPERATING EXPENSES	'	'	'	'	'	'
Operating and maintenance	8.8	9.1	23.2	26.4	32	33.6
General and administrative	10.8	12	35.3	36.5	48.8	49.3
Retirement incentive	0	0	0	0	0.9	0
Depreciation and amortization	14	13.6	42.2	40.6	55.9	53.9
Asset impairment	80.6	0	80.6	0	80.6	0
Other taxes	2.5	2.4	7.4	7.3	9.2	9.4
Cost of sales (excluding operating expenses shown separately)	0.5	0.7	2.7	1.9	7.5	2.7
Total Operating Expenses	117.2	37.8	191.4	112.7	234.9	148.9
Net gain (loss) from asset sales	0	2.5	0	2.6	0.1	2.6
OPERATING INCOME (LOSS)	-52.6	32.6	5.7	95.2	34.5	126.2
Interest and other income	0.6	0	1.2	0.3	1.5	0
Income from unconsolidated affiliate	0.9	1	2.8	2.8	3.7	3.7
Interest expense	-6.5	-6.6	-19.5	-19.8	-26	-24.8
INCOME (LOSS) BEFORE INCOME TAXES	-57.6	27	-9.8	78.5	13.7	105.1
Income taxes	19.7	-9.9	2.2	-28.7	-6.4	-38.1
NET INCOME (LOSS)	($37.90)	$17.10	($7.60)	$49.80	$7.30	$67

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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net income (loss)	($19.20)	$33.80	$93.10	$148.20	$156.90	$209.80
Other comprehensive income (loss):	'	'	'	'	'	'
Pension and other postretirement benefits	9	6.6	24.7	19.8	-28.1	-150.6
Interest rate cash flow hedges	0.1	0.2	0.4	0.4	0.4	-0.6
Change in fair value of long-term investment	0	0.1	-0.1	0.1	-0.1	0.1
Income taxes	-3.4	-2.8	-9.4	-7.9	10.8	57.7
Net other comprehensive income (loss)	5.7	4.1	15.6	12.4	-17	-93.4
COMPREHENSIVE INCOME (LOSS)	-13.5	37.9	108.7	160.6	139.9	116.4
Questar Pipeline [Member]	'	'	'	'	'	'
Net income (loss)	-37.9	17.1	-7.6	49.8	7.3	67
Other comprehensive income (loss):	'	'	'	'	'	'
Interest rate cash flow hedges	0.1	0.2	0.4	0.4	0.4	-0.6
Income taxes	0	-0.1	-0.1	-0.2	-0.1	0.2
Net other comprehensive income (loss)	0.1	0.1	0.3	0.2	0.3	-0.4
COMPREHENSIVE INCOME (LOSS)	($37.80)	$17.20	($7.30)	$50	$7.60	$66.60

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Current Assets	'	'	'
Cash and cash equivalents	$0	$16,800,000	$0
Accounts receivable, net	58,000,000	114,300,000	60,000,000
Unbilled gas accounts receivable	11,700,000	78,300,000	10,600,000
Gas stored underground	59,400,000	39,000,000	62,100,000
Materials and supplies	24,000,000	24,500,000	25,700,000
Current regulatory assets	49,300,000	46,700,000	56,800,000
Prepaid expenses and other	6,000,000	13,100,000	6,500,000
Deferred income taxes - current	8,800,000	13,000,000	6,500,000
Total Current Assets	217,200,000	345,700,000	228,200,000
Property, Plant and Equipment	5,583,800,000	5,333,300,000	5,244,400,000
Accumulated depreciation, depletion and amortization	-2,088,800,000	-2,016,300,000	-1,983,200,000
Net Property, Plant and Equipment	3,495,000,000	3,317,000,000	3,261,200,000
Investment in unconsolidated affiliate	25,800,000	26,500,000	26,800,000
Noncurrent regulatory assets	21,300,000	21,600,000	21,700,000
Other noncurrent assets	50,900,000	46,300,000	44,500,000
TOTAL ASSETS	3,810,200,000	3,757,100,000	3,582,400,000
Current Liabilities	'	'	'
Checks outstanding in excess of cash balances	1,600,000	0	5,400,000
Short-term debt	355,000,000	263,000,000	263,000,000
Accounts payable and accrued expenses	211,600,000	235,200,000	215,600,000
Current regulatory liabilities	1,800,000	5,800,000	4,300,000
Current portion of long-term debt and capital lease obligation	800,000	42,700,000	109,200,000
Total Current Liabilities	570,800,000	546,700,000	597,500,000
Long-term debt and capital lease obligation, less current portion	1,136,100,000	1,138,200,000	988,900,000
Deferred income taxes	645,900,000	603,400,000	563,500,000
Asset retirement obligations	65,900,000	67,200,000	66,300,000
Defined benefit pension plan and other postretirement benefits	257,300,000	303,700,000	246,900,000
Customer contributions in aid of construction	31,500,000	22,900,000	30,400,000
Regulatory and other noncurrent liabilities	44,100,000	39,400,000	39,300,000
COMMON SHAREHOLDERS' EQUITY	'	'	'
Common stock	449,700,000	442,400,000	457,800,000
Retained earnings	839,600,000	839,500,000	805,500,000
Accumulated other comprehensive (loss)	-230,700,000	-246,300,000	-213,700,000
Total Common Shareholders' Equity	1,058,600,000	1,035,600,000	1,049,600,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	3,810,200,000	3,757,100,000	3,582,400,000
Questar Gas [Member]	'	'	'
Current Assets	'	'	'
Cash and cash equivalents	0	1,400,000	0
Accounts receivable, net	24,200,000	67,000,000	26,900,000
Unbilled gas accounts receivable	11,700,000	78,200,000	10,500,000
Accounts receivable from affiliates	31,400,000	31,800,000	22,200,000
Gas stored underground	56,500,000	38,300,000	58,400,000
Materials and supplies	12,200,000	13,500,000	13,500,000
Current regulatory assets	45,500,000	41,000,000	52,400,000
Prepaid expenses and other	2,400,000	3,200,000	2,800,000
Deferred income taxes - current	1,500,000	1,500,000	0
Total Current Assets	185,400,000	275,900,000	186,700,000
Property, Plant and Equipment	2,147,800,000	2,040,900,000	2,013,600,000
Accumulated depreciation, depletion and amortization	-790,300,000	-762,800,000	-758,600,000
Net Property, Plant and Equipment	1,357,500,000	1,278,100,000	1,255,000,000
Noncurrent regulatory assets	16,500,000	16,400,000	16,000,000
Goodwill	5,600,000	5,600,000	5,600,000
Other noncurrent assets	3,000,000	3,100,000	2,100,000
TOTAL ASSETS	1,568,000,000	1,579,100,000	1,465,400,000
Current Liabilities	'	'	'
Checks outstanding in excess of cash balances	1,400,000	0	2,000,000
Notes payable to Questar	195,000,000	166,100,000	206,600,000
Accounts payable and accrued expenses	80,300,000	105,000,000	72,800,000
Accounts payable to affiliates	49,900,000	50,900,000	46,200,000
Customer advances	21,900,000	30,200,000	32,200,000
Current regulatory liabilities	500,000	4,300,000	1,800,000
Deferred income taxes - current	0	0	4,000,000
Current portion of long-term debt and capital lease obligation	0	42,000,000	108,500,000
Total Current Liabilities	349,000,000	398,500,000	474,100,000
Long-term debt and capital lease obligation, less current portion	384,500,000	384,500,000	234,500,000
Deferred income taxes	330,700,000	301,600,000	270,800,000
Customer contributions in aid of construction	31,500,000	22,900,000	30,400,000
Regulatory and other noncurrent liabilities	3,400,000	4,000,000	3,800,000
COMMON SHAREHOLDERS' EQUITY	'	'	'
Common stock	23,000,000	23,000,000	23,000,000
Additional paid-in capital	173,600,000	172,500,000	172,200,000
Retained earnings	272,300,000	272,100,000	256,600,000
Total Common Shareholders' Equity	468,900,000	467,600,000	451,800,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	1,568,000,000	1,579,100,000	1,465,400,000
Questar Pipeline [Member]	'	'	'
Current Assets	'	'	'
Cash and cash equivalents	1,500,000	7,100,000	400,000
Notes receivable from Questar	36,600,000	38,700,000	42,000,000
Accounts receivable, net	17,800,000	19,100,000	19,800,000
Accounts receivable from affiliates	32,700,000	27,500,000	28,200,000
Gas stored underground	2,900,000	700,000	3,700,000
Materials and supplies	7,500,000	6,500,000	7,000,000
Current regulatory assets	3,800,000	5,700,000	4,400,000
Prepaid expenses and other	1,800,000	7,700,000	1,900,000
Deferred income taxes - current	1,600,000	1,600,000	1,800,000
Total Current Assets	106,200,000	114,600,000	109,200,000
Property, Plant and Equipment	1,766,100,000	1,840,100,000	1,821,900,000
Accumulated depreciation, depletion and amortization	-617,800,000	-629,300,000	-618,700,000
Net Property, Plant and Equipment	1,148,300,000	1,210,800,000	1,203,200,000
Investment in unconsolidated affiliate	25,800,000	26,500,000	26,800,000
Goodwill	4,200,000	4,200,000	4,200,000
Regulatory and other noncurrent assets	8,200,000	9,000,000	9,500,000
TOTAL ASSETS	1,292,700,000	1,365,100,000	1,352,900,000
Current Liabilities	'	'	'
Accounts payable and accrued expenses	35,900,000	25,700,000	66,500,000
Accounts payable to affiliates	3,700,000	16,900,000	3,200,000
Current regulatory liabilities	1,300,000	1,500,000	2,500,000
Total Current Liabilities	40,900,000	44,100,000	72,200,000
Long-term debt and capital lease obligation, less current portion	458,800,000	458,900,000	458,900,000
Deferred income taxes	226,900,000	242,500,000	201,800,000
Regulatory and other noncurrent liabilities	13,900,000	13,800,000	13,800,000
COMMON SHAREHOLDERS' EQUITY	'	'	'
Common stock	6,600,000	6,600,000	6,600,000
Additional paid-in capital	349,200,000	347,500,000	347,100,000
Retained earnings	219,300,000	274,900,000	275,700,000
Accumulated other comprehensive (loss)	-22,900,000	-23,200,000	-23,200,000
Total Common Shareholders' Equity	552,200,000	605,800,000	606,200,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	$1,292,700,000	$1,365,100,000	$1,352,900,000

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
OPERATING ACTIVITIES	'	'
Net income (loss)	$93.10	$148.20
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation, depletion and amortization	148.7	141.3
Deferred income taxes	37.2	65.1
Asset impairment	80.6	0
Share-based compensation	7.7	7.5
Net (gain) from asset sales	-0.1	-5.1
(Income) from unconsolidated affiliate	-2.8	-2.8
Distributions from unconsolidated affiliate and other	4.2	3.7
Changes in operating assets and liabilities	55.4	28.1
Net Cash Provided By Operating Activities	424	386
INVESTING ACTIVITIES	'	'
Property, plant and equipment	-287.4	-276.1
Wexpro acquisition of producing properties	-106.7	0
Cash used in disposition of assets	-3.1	-2.5
Proceeds from disposition of assets	0.6	4.5
Net Cash Used In Investing Activities	-396.6	-274.1
FINANCING ACTIVITIES	'	'
Common stock issued	2.2	4.7
Common stock repurchased	-4.2	-72.5
Change in short-term debt	92	44
Long-term debt and capital lease obligation repaid	-42.6	-25.6
Long-term debt issuance costs	-1.7	0
Checks outstanding in excess of cash balances	1.6	5.4
Dividends paid	-93	-87.6
Tax benefits from share-based compensation	1.5	8.1
Net Cash Provided By (Used In) Financing Activities	-44.2	-123.5
Change in cash and cash equivalents	-16.8	-11.6
Beginning cash and cash equivalents	16.8	11.6
Ending cash and cash equivalents	0	0
Supplemental Disclosure of Noncash Investing and Financing Transaction:	'	'
Capital lease obligation incurred	'	40.8
Questar Gas [Member]	'	'
OPERATING ACTIVITIES	'	'
Net income (loss)	26.8	23.3
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and amortization	40.7	38.7
Deferred income taxes	29.1	20.6
Share-based compensation	1.1	0.9
Changes in operating assets and liabilities	49.9	17.6
Net Cash Provided By Operating Activities	147.6	101.1
INVESTING ACTIVITIES	'	'
Property, plant and equipment	-119.3	-120.8
Cash used in disposition of assets	-2.5	-1.8
Proceeds from disposition of assets	0.3	0.3
Affiliated-company property, plant and equipment transfers	10.8	0
Net Cash Used In Investing Activities	-110.7	-122.3
FINANCING ACTIVITIES	'	'
Long-term debt and capital lease obligation repaid	-42	-25
Change in notes payable to Questar	28.9	63.9
Checks outstanding in excess of cash balances	1.4	2
Dividends paid	-26.6	-24.7
Net Cash Provided By (Used In) Financing Activities	-38.3	16.2
Change in cash and cash equivalents	-1.4	-5
Beginning cash and cash equivalents	1.4	5
Ending cash and cash equivalents	0	0
Questar Pipeline [Member]	'	'
OPERATING ACTIVITIES	'	'
Net income (loss)	-7.6	49.8
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and amortization	44.1	42.5
Deferred income taxes	-15.7	5
Asset impairment	80.6	0
Share-based compensation	1.6	1.5
Net (gain) from asset sales	0	-2.6
(Income) from unconsolidated affiliate	-2.8	-2.8
Distributions from unconsolidated affiliate and other	3.9	3.7
Changes in operating assets and liabilities	3.6	18.5
Net Cash Provided By Operating Activities	107.7	115.6
INVESTING ACTIVITIES	'	'
Property, plant and equipment	-56.2	-41.6
Cash used in disposition of assets	-0.6	-0.7
Proceeds from disposition of assets	0.1	4.2
Affiliated-company property, plant and equipment transfers	-10.7	0
Net Cash Used In Investing Activities	-67.4	-38.1
FINANCING ACTIVITIES	'	'
Change in notes receivable from Questar	2.1	-33.2
Dividends paid	-48	-47.3
Net Cash Provided By (Used In) Financing Activities	-45.9	-80.5
Change in cash and cash equivalents	-5.6	-3
Beginning cash and cash equivalents	7.1	3.4
Ending cash and cash equivalents	$1.50	$0.40

Nature_of_Business

Nature of Business	9 Months Ended
	Sep. 30, 2013
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	9 Months Ended
	Sep. 30, 2013
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, 2012.
	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, 2013, are not necessarily indicative of the results that may be expected for the year ending December 31, 2013.
	Certain reclassifications were made to prior year information to conform to the current year presentation. This includes reclassifications on the Questar Condensed Consolidated Statements of Comprehensive Income and Condensed Consolidated Balance Sheets to reflect revised accounting for reclassifications out of accumulated other comprehensive loss related to the Company's pension and other postretirement benefit plans.
	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. 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,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Questar Gas
	Gas purchases	$	0.1		$	—		$	113.7		$	64.3		$	153.6		$	131.5
	Operator service fee	68.2			69.3			215.2			204.5			284.7			271.6
	Transportation and storage	18.5			19			58.6			58.5			79.7			78.6
	Gathering	4.5			4.8			13.6			16			18.1			22.3
	Royalties	11			7			32.4			23.4			41			34.3
	Storage (injection) withdrawal, net	(37.3		)	(29.0		)	(18.1		)	(18.1		)	1.9			(8.8		)
	Purchased-gas account adjustment	(15.9		)	(27.6		)	5.1			4			17.2			17.1
	Other	1			1.2			3.7			3.8			4.9			5
	Total Questar Gas cost of natural gas sold	50.1			44.7			424.2			356.4			601.1			551.6
	Elimination of Questar Gas cost of natural gas sold - affiliated parties	(85.6		)	(87.5		)	(269.5		)	(259.2		)	(358.0		)	(344.8		)
	Total Questar Gas cost of natural gas sold - unaffiliated parties	(35.5		)	(42.8		)	154.7			97.2			243.1			206.8
	Questar Pipeline
	Total Questar Pipeline cost of sales	0.5			0.7			2.7			1.9			7.5			2.7
	Total cost of sales	$	(35.0	)	$	(42.1	)	$	157.4		$	99.1		$	250.6		$	209.5

Comprehensive_Income

Comprehensive Income	9 Months Ended
	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'
Comprehensive Income	'
	Note 3 - Comprehensive Income
	Beginning in 2012, the Company and its subsidiaries adopted accounting guidance issued in June 2011 that resulted in the addition of statements of comprehensive income to the primary financial statements. Beginning in 2013, the Company and its subsidiaries adopted accounting guidance issued in February 2013 that requires additional disclosures about reclassifications from accumulated other comprehensive income into earnings.
	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 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 or 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 table below. The table also discloses 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											9 Months Ended
		September 30, 2013											September 30, 2013
		(in millions)
	AOCI at beginning of period	$	(213.5	)	$	(23.0	)	$	0.1	$	(236.4	)	$	(223.2	)	$	(23.2	)	$	0.1		$	(246.3	)
	OCI before reclassifications	—			—			—		—			—			—			(0.1		)	(0.1		)
	Reclassified from AOCI(1)	9			0.1			—		9.1			24.7			0.4			—			25.1
	Income taxes
	OCI before reclassifications	—			—			—		—			—			—			0.1			0.1
	Reclassified from AOCI(2)	(3.4		)	—			—		(3.4		)	(9.4		)	(0.1		)	—			(9.5		)
	Total income taxes	(3.4		)	—			—		(3.4		)	(9.4		)	(0.1		)	0.1			(9.4		)
	Net other comprehensive income	5.6			0.1			—		5.7			15.3			0.3			—			15.6
	AOCI at September 30, 2013	$	(207.9	)	$	(22.9	)	$	0.1	$	(230.7	)	$	(207.9	)	$	(22.9	)	$	0.1		$	(230.7	)
	(1) Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income.
	(2) 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 benefits 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 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 income taxes and income statement reclassifications effects, apply to Questar Pipeline.

Earnings_Per_Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	Note 4 - 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. 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 restricted stock units (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 earnings (loss) per share. 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,
		2013	2012	2013	2012	2013	2012
		(in millions)
	Weighted-average basic common shares outstanding	175.5	175.4	175.4	177	175.5	177.2
	Potential number of shares issuable under the Company's LTSIP	—	1.1	0.7	1.1	0.6	1.1
	Weighted-average diluted common shares outstanding	175.5	176.5	176.1	178.1	176.1	178.3
	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.

Asset_Retirement_Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2013
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 in 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,
		2013			2012
		(in millions)
	AROs at beginning of year	$	67.2		$	63.8
	Accretion	2.4			2.3
	Liabilities incurred	4.2			2.2
	Revisions in estimated cash flows	(6.8		)	(1.2		)
	Liabilities settled	(1.1		)	(0.8		)
	AROs at September 30,	$	65.9		$	66.3
	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 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

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Note 6 - Fair Value Measurements
	Questar complies with the accounting standards for fair value measurements and disclosures. The standards establish a fair value hierarchy. Level 1 inputs are unadjusted quoted prices for identical assets or liabilities in active markets that the Company has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 inputs are unobservable inputs for the asset or liability. The Company had no assets or liabilities measured using Level 3 inputs at September 30, 2013, September 30, 2012 or December 31, 2012.
	Beginning in 2012, Questar adopted fair value accounting guidance issued in May 2011. The guidance did not result in any changes to the reported amounts of assets or liabilities, but did result in disclosure of the fair value hierarchy levels associated with fair value estimates for financial assets and liabilities not carried at fair value.
	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, 2013				Sept. 30, 2012				Dec. 31, 2012
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	—	$	—	$	16.8	$	16.8
	Long-term investment	1	16.8		16.8		15		15		15.5		15.5
	Financial liabilities
	Checks outstanding in excess of cash balances	1	1.6		1.6		5.4		5.4		—		—
	Short-term debt	1	355		355		263		263		263		263
	Long-term debt, including current portion	2	1,097.50		1,191.10		1,057.90		1,237.50		1,140.90		1,303.10
	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, 2013				Sept. 30, 2012				Dec. 31, 2012
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	—	$	—	$	1.4	$	1.4
	Financial liabilities
	Checks outstanding in excess of cash balances	1	1.4		1.4		2		2		—		—
	Notes payable to Questar	1	195		195		206.6		206.6		166.1		166.1
	Long-term debt, including current portion	2	384.5		425.6		343		426.3		426.5		503.7
	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 variable 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, 2013				Sept. 30, 2012				Dec. 31, 2012
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	1.5	$	1.5	$	0.4	$	0.4	$	7.1	$	7.1
	Notes receivable from Questar	1	36.6		36.6		42		42		38.7		38.7
	Financial liabilities
	Long-term debt	2	458.8		505.5		458.9		547.8		458.9		536.6
	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 variable 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 include 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 is based on inputs that indicate overall negative future net cash flows. Questar used a probability-weighted discounted cash flow analysis that included significant inputs including Questar's cost of capital and assumptions regarding future transportation rates and operating costs. This is a Level 3 fair value measurement because the inputs are unobservable. Based on this analysis, Questar determined that the asset was impaired. See Note 12 for additional information.

Derivative_Instruments_and_Hed

Derivative Instruments and Hedging Activities	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative Instruments and Hedging Activities	'
	Note 7 - Derivative Instruments and Hedging Activities
	Questar and its subsidiaries may enter into derivative instruments to manage exposure to changes in current and future market interest rates. In order to mitigate its exposure to changes in the fair value of its fixed-rate corporate debt resulting from changes in benchmark interest rates, in the second quarter of 2011 Questar executed a fixed-to-floating interest rate swap transaction with a counterparty and converted $125.0 million of its 2.75% fixed-rate long-term debt to floating-rate debt. The 2.75% rate was swapped for a London Interbank Offered Rate (LIBOR)-based floating rate. Questar terminated and settled this hedge transaction in March 2012, for a deferred gain of $7.2 million, which is being amortized to interest expense through the maturity of the notes in 2016. Prior to its termination, this swap was accounted for as a fair value hedge under the accounting standards for derivatives and hedging.
	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. The swaps were also treated as qualifying hedging transactions for income tax purposes.
	The following table presents the pre-tax effects of the derivative instruments designated as a fair value hedge (including the hedged item) and cash flow hedges on the Consolidated Statements of Income as well as the pre-tax effects of the derivative instruments designated as cash flow hedges on OCI:
			3 Months Ended						9 Months Ended						12 Months Ended
		Financial Statement Location of Gain (Loss)	September 30,						September 30,						September 30,
	Instrument and Activity		2013			2012			2013			2012			2013			2012
			(in millions)
	Fair Value Hedge
	Questar Corporation
	Interest rate derivative instrument
	Realized gain	Interest expense	$	—		$	—		$	—		$	—		$	—		$	0.7
	2.75% Notes due 2016
	Unrealized loss	Interest expense	—			—			—			—			—			(0.7		)
	Cash Flow Hedges
	Questar Pipeline
	Interest rate derivative instruments
	Deferrals of effective portions	OCI	—			—			—			—			—			(1.1		)
	Losses reclassified from AOCI into earnings for effective portions	Interest expense	(0.1		)	(0.2		)	(0.4		)	(0.4		)	(0.4		)	(0.5		)
	There was no ineffectiveness recognized on the fair value hedge for the three, nine and 12 months ended September 30, 2013 and 2012. There was no ineffectiveness recognized on the cash flow hedges for the three and nine months ended September 30, 2013 and 2012 and the 12 months ended September 30, 2013. Ineffectiveness recognized on the cash flow hedges was de minimis in the 12 months ended September 30, 2012. 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 $0.5 million are expected to be reclassified from AOCI to the Consolidated Statements of Income in the next 12 months. As of September 30, 2013, 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, 2013, September 30, 2012 or December 31, 2012.

ShareBased_Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2013
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 officers, employees and non-employee directors under its LTSIP. Questar recognizes expense over time as the stock options, restricted shares, RSUs and performance shares vest. Total share-based compensation expense amounted to $7.7 million for the first nine months of 2013 compared to $7.5 million in 2012. Deferred share-based compensation, representing the unvested value of restricted share and RSU awards, amounted to $6.5 million at September 30, 2013. For the first nine months, cash flow from income tax benefits in excess of recognized compensation expense amounted to $1.5 million in 2013 compared to $8.1 million in 2012. There were 5,577,106 shares available for future grants at September 30, 2013.
	Unvested stock options decreased by 29,398 shares to zero shares in the first nine months of 2013. No stock options were granted in the first nine months of 2013. Stock option transactions under the terms of the LTSIP are summarized below:
		Options			Exercise						Weighted-Average Exercise Price
		Outstanding			Price Range
	Balance at December 31, 2012	770,923			$	4.37	-	$	17.35		$	11.35
	Exercised	(53,083	)		4.37		-	13.1			4.75
	Balance at September 30, 2013	717,840			$	7.84	-	$	17.35		$	11.84
	Options Outstanding													Options Exercisable
	Range of exercise							Number outstanding at Sept. 30, 2013		Weighted-average remaining term in years		Weighted-average exercise price		Number exercisable at Sept. 30, 2013	Weighted-average exercise price
	prices
	$	7.84		-	$	11.4		404,174		2.1		$	10.52	404,174	$	10.52
	13.1			-	17.35			313,666		2.8		13.54		313,666	13.54
								717,840		2.4		$	11.84	717,840	$	11.84
	Restricted share grants typically vest in equal installments over a three- or four-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, 2013, was 11 months. 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, 2012	810,342			$	13.1	-	$	20.9		$	17.74
	Granted	658			21.53			21.53			21.53
	Vested	(417,882	)		13.1		-	20.9			17.24
	Balance at September 30, 2013	393,118			$	13.1	-	$	21.53		$	18.29
	Starting in the first quarter of 2013, Questar granted RSUs to certain officers, employees and non-employee directors under its 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, 2013, was 17 months.
	Transactions involving RSUs under the terms of the LTSIP are summarized below:
		RSUs			Price Range						Weighted-Average Price
		Outstanding
	Granted	326,797			$	22.17	-	$	25.44		$	23.63
	Vested	(12,522	)		23.62			23.62			23.62
	Balance at September 30, 2013	314,275			$	22.17	-	$	25.44		$	23.63
	Grants of RSUs with deferred share distributions (deferred RSUs) typically vest in equal installments over a three-year period from the grant date. At September 30, 2013, Questar's outstanding deferred RSUs totaled 73,071 with a weighted-average price of $15.67 per share. The deferred RSUs were fully vested as of July 1, 2013. One share of Questar common stock will be distributed for each vested deferred RSU (including accrued reinvested dividend equivalents) at the time of the grantee's separation from service.
	Questar grants performance shares to certain Company executive officers under the terms of the LTSIP. The awards are designed to motivate and reward these executives for long-term Company performance and provide an incentive for them to remain with the Company. The target number of performance shares for each executive 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 executive officer was employed by the Company or its affiliates as of the last day of the performance period.
	Half of any award will be distributed in shares of Questar common stock and half in cash. The Monte Carlo simulation method was 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 $1.2 million in the first nine months of 2013 and $1.4 million in the first nine months of 2012. The weighted-average remaining vesting period of unvested performance shares at September 30, 2013, 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, 2012	264,867			$	18.23	-	$	25.42		$	21.94
	Granted	126,606			39.62			39.62			39.62
	Forfeited	(3,594	)		18.23		-	39.62			33.09
	Balance at September 30, 2013	387,879			$	18.23	-	$	39.62		$	27.61
	The above September 30, 2013 balance includes 5,330 vested target performance shares with a weighted-average grant-date fair value of $23.39 and expected distribution dates ranging from the first quarter of 2014 through the first quarter of 2016.

Operations_by_Line_of_Business

Operations by Line of Business	9 Months Ended
	Sep. 30, 2013
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,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Revenues from Unaffiliated Customers
	Questar Gas	$	89.4		$	82.5		$	647.8		$	578.7		$	928.8		$	876.5
	Wexpro	13.2			9.8			32			27.1			41			35.5
	Questar Pipeline	47			49.5			142.3			150.1			195.3			198.7
	Total	$	149.6		$	141.8		$	822.1		$	755.9		$	1,165.10		$	1,110.70
	Revenues from Affiliated Companies
	Questar Gas	$	0.2		$	0.5		$	0.6		$	2.3		$	0.8		$	3.4
	Wexpro	68.1			69.3			215.2			204.6			284.7			271.8
	Questar Pipeline	17.6			18.4			54.8			55.2			74			73.8
	Total	$	85.9		$	88.2		$	270.6		$	262.1		$	359.5		$	349
	Operating Income (Loss)
	Questar Gas	$	(11.2	)	$	(10.7	)	$	55.3		$	52.6		$	95.6		$	90.1
	Wexpro	40.7			41			121.9			117.9			162.1			155.3
	Questar Pipeline	(52.6		)	32.6			5.7			95.2			34.5			126.2
	Corporate and other	3.7			0.7			0.3			1.4			(0.4		)	2.1
	Total	$	(19.4	)	$	63.6		$	183.2		$	267.1		$	291.8		$	373.7
	Net Income (Loss)
	Questar Gas	$	(9.0	)	$	(9.3	)	$	26.8		$	23.3		$	50.6		$	43.5
	Wexpro	27.5			26.4			82.2			76.5			109.6			100.1
	Questar Pipeline	(37.9		)	17.1			(7.6		)	49.8			7.3			67
	Corporate and other	0.2			(0.4		)	(8.3		)	(1.4		)	(10.6		)	(0.8		)
	Total	$	(19.2	)	$	33.8		$	93.1		$	148.2		$	156.9		$	209.8

Employee_Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2013
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 2013 estimated net cost for the qualified pension plan is $32.0 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 for the qualified plan. The nonqualified pension plan is unfunded; claims are paid from the Company's general funds. The 2013 estimated net cost for the nonqualified pension plan is $4.3 million. Components of the qualified and nonqualified net pension cost included in the determination of net income (loss) are listed in the table below:
		3 Months Ended						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Service cost	$	3.2		$	3.2		$	10		$	9.7		$	13.5		$	12.4
	Interest cost	7.6			7.8			23.4			23.3			31.2			30.5
	Expected return on plan assets	(9.5		)	(8.0		)	(28.6		)	(23.7		)	(36.7		)	(30.8		)
	Prior service and other costs	0.2			0.4			0.8			1.1			0.8			2.1
	Recognized net actuarial loss	8			5.4			21.7			16.2			30.4			20.5
	Net pension cost	$	9.5		$	8.8		$	27.3		$	26.6		$	39.2		$	34.7
	The Company currently estimates a $5.0 million net cost for postretirement benefits other than pensions in 2013 before accretion of a regulatory liability. Net 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,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Service cost	$	0.2		$	0.2		$	0.6		$	0.5		$	0.8		$	0.5
	Interest cost	0.9			1			2.8			2.8			3.8			3.7
	Expected return on plan assets	(0.6		)	(0.6		)	(1.9		)	(1.7		)	(2.5		)	(2.3		)
	Amortization of transition obligation	—			0.4			—			1.2			0.4			1.8
	Recognized net actuarial loss	0.8			0.5			2.2			1.6			3.1			1.4
	Accretion of regulatory liability	0.1			0.1			0.5			0.5			0.3			0.6
	Net postretirement benefit cost	$	1.4		$	1.6		$	4.2		$	4.9		$	5.9		$	5.7

Debt

Debt	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Abstract]	'
Debt	'
	Note 11 - Debt
	The Company has a revolving credit facility with various lenders to provide back-up credit liquidity support for its commercial paper program. Credit commitments under this revolving credit facility totaled $750.0 million at September 30, 2013, with no amounts borrowed. This revolving credit facility has interest-rate options generally below the prime interest rate and carries commitment fees on the unused balance. In April 2013, Questar amended and restated its revolving credit facility to increase its size from $500.0 million to $750.0 million and extend its maturity from August 31, 2016 to April 19, 2018. Under the facility, consolidated funded debt cannot exceed 70% of consolidated capitalization. Commercial paper outstanding amounted to $355.0 million at September 30, 2013, $263.0 million at September 30, 2012 and $263.0 million at December 31, 2012.
	During the third quarter of 2013, Questar Gas entered into a commitment to borrow $150 million of long-term debt in the private placement market to be funded in December 2013. Questar Gas will issue $90 million of 30-year notes with an interest rate of 4.78% and $60 million of 35-year notes with an interest rate of 4.83%. Proceeds from the debt issuance will be used to repay existing indebtedness and for general corporate purposes.
	Except for the amendment and restatement to the Company's revolving credit facility and the Questar Gas borrowing commitment, there have not been any significant new borrowings or modifications of existing financing arrangements at Questar, Questar Gas or Questar Pipeline since December 31, 2012.

Strategic_Review_of_Questar_So

Strategic Review of Questar Southern Trails Pipeline and Impairment of Eastern Segment	9 Months Ended
	Sep. 30, 2013
Strategic Review of Questar Southern Trails Pipeline and Impairment of Eastern Segment [Abstract]	'
Strategic Review of Questar Southern Trails Pipeline and Impairment of Eastern Segment	'
	Note 12 - Strategic Review of Questar Southern Trails Pipeline and Impairment of Eastern Segment
	In the fourth quarter of 2012, Questar Pipeline initiated a strategic review of the noncore Questar Southern Trails Pipeline. All strategic options were analyzed, including joint ventures, asset sales or other alternatives. The western segment of Southern Trails Pipeline runs 96 miles from Whitewater to Long Beach, California. This segment has not been placed in service. The eastern segment of Southern Trails Pipeline runs 487 miles from the San Juan Basin in New Mexico to connections with other pipelines in the eastern portion of southern California.
	As a result of that review, Questar Pipeline entered into an agreement with another pipeline company to evaluate and potentially recommission the western portion of its Southern Trails Pipeline to its original purpose as a crude oil transport pipeline and to develop a rail terminal to offload crude from railcars and into the pipeline for transportation to refineries in Long Beach, California. Questar Pipeline's net book value of the western segment of Southern Trails Pipeline is approximately $21 million. This project is in the marketing phase and a decision whether or not to proceed with the development is expected in 2014.
	Questar has been in discussions with a third party developer to either purchase the eastern segment of Southern Trails Pipeline or enter into a long-term transportation contract for the full capacity of the pipeline. The expected progress with this party to reach a definitive agreement was not achieved during the third quarter of 2013. In addition during the third quarter, Questar updated its five-year forecast for 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 do not cover these increasing operating expenses. Due to the developments in the third quarter of 2013, 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 used a probability-weighted discounted cash flow analysis that included significant inputs including Questar's cost of capital and assumptions regarding future transportation rates and operating costs.

Wexpro_Acquisition_of_Producin

Wexpro Acquisition of Producing Properties	9 Months Ended
	Sep. 30, 2013
Wexpro Acquisition of Producing Properties [Abstract]	'
Wexpro Acquisition of Producing Properties	'
	Note 13 - Wexpro Acquisition of Producing Properties
	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 for $106.7 million (Trail acquisition). This is a “bolt-on” acquisition to the company’s current Trail assets, which are governed by the 1981 Wexpro Agreement. The Company is in the process of submitting these properties to the public service commissions of Utah and Wyoming for inclusion as cost-of-service properties under the Wexpro II Agreement.
	Because it contains proved properties, the Trail acquisition is accounted for using the accounting guidance for business combinations. Summary information related to the Trail acquisition is shown in the table below. Amounts are provisional and are subject to post-closing adjustments.
		(in millions)
	Fair value of consideration transferred:
	Cash paid at closing	$	106.7
	Recognized amounts of identifiable assets acquired and liabilities assumed, at fair value:
	Proved properties	$	108.8
	Asset retirement obligations	(2.1		)
	Total fair value of identifiable net assets acquired	$	106.7
	Revenues of $1.5 million and net income of $0.3 million attributable to the Trail acquisition are included in Questar's Condensed Consolidated Statements of Income for the period between the September 4, 2013 closing date and September 30, 2013. Trail acquisition-related transaction costs of $0.2 million for the first nine months of 2013 are included in general and administrative expense on Questar's Condensed Consolidated Statement of Income. Supplemental pro forma income information related to the Trail acquisition is not presented because it is immaterial to Questar's consolidated revenues, expenses and income in all periods presented.

Basis_of_Presentation_of_Inter1

Basis of Presentation of Interim Financial Statements (Policies)	9 Months Ended
	Sep. 30, 2013
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).
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 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 or 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 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.
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. 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 restricted stock units (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 earnings (loss) per share. The application of the two-class method had an insignificant impact on the calculation of both basic and diluted EPS.
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 in 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, 2013
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,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Questar Gas
	Gas purchases	$	0.1		$	—		$	113.7		$	64.3		$	153.6		$	131.5
	Operator service fee	68.2			69.3			215.2			204.5			284.7			271.6
	Transportation and storage	18.5			19			58.6			58.5			79.7			78.6
	Gathering	4.5			4.8			13.6			16			18.1			22.3
	Royalties	11			7			32.4			23.4			41			34.3
	Storage (injection) withdrawal, net	(37.3		)	(29.0		)	(18.1		)	(18.1		)	1.9			(8.8		)
	Purchased-gas account adjustment	(15.9		)	(27.6		)	5.1			4			17.2			17.1
	Other	1			1.2			3.7			3.8			4.9			5
	Total Questar Gas cost of natural gas sold	50.1			44.7			424.2			356.4			601.1			551.6
	Elimination of Questar Gas cost of natural gas sold - affiliated parties	(85.6		)	(87.5		)	(269.5		)	(259.2		)	(358.0		)	(344.8		)
	Total Questar Gas cost of natural gas sold - unaffiliated parties	(35.5		)	(42.8		)	154.7			97.2			243.1			206.8
	Questar Pipeline
	Total Questar Pipeline cost of sales	0.5			0.7			2.7			1.9			7.5			2.7
	Total cost of sales	$	(35.0	)	$	(42.1	)	$	157.4		$	99.1		$	250.6		$	209.5

Comprehensive_Income_Tables

Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2013
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 table below. The table also discloses 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											9 Months Ended
		September 30, 2013											September 30, 2013
		(in millions)
	AOCI at beginning of period	$	(213.5	)	$	(23.0	)	$	0.1	$	(236.4	)	$	(223.2	)	$	(23.2	)	$	0.1		$	(246.3	)
	OCI before reclassifications	—			—			—		—			—			—			(0.1		)	(0.1		)
	Reclassified from AOCI(1)	9			0.1			—		9.1			24.7			0.4			—			25.1
	Income taxes
	OCI before reclassifications	—			—			—		—			—			—			0.1			0.1
	Reclassified from AOCI(2)	(3.4		)	—			—		(3.4		)	(9.4		)	(0.1		)	—			(9.5		)
	Total income taxes	(3.4		)	—			—		(3.4		)	(9.4		)	(0.1		)	0.1			(9.4		)
	Net other comprehensive income	5.6			0.1			—		5.7			15.3			0.3			—			15.6
	AOCI at September 30, 2013	$	(207.9	)	$	(22.9	)	$	0.1	$	(230.7	)	$	(207.9	)	$	(22.9	)	$	0.1		$	(230.7	)
	(1) Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income.
	(2) Interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income.

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2013
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,
		2013	2012	2013	2012	2013	2012
		(in millions)
	Weighted-average basic common shares outstanding	175.5	175.4	175.4	177	175.5	177.2
	Potential number of shares issuable under the Company's LTSIP	—	1.1	0.7	1.1	0.6	1.1
	Weighted-average diluted common shares outstanding	175.5	176.5	176.1	178.1	176.1	178.3

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2013
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,
		2013			2012
		(in millions)
	AROs at beginning of year	$	67.2		$	63.8
	Accretion	2.4			2.3
	Liabilities incurred	4.2			2.2
	Revisions in estimated cash flows	(6.8		)	(1.2		)
	Liabilities settled	(1.1		)	(0.8		)
	AROs at September 30,	$	65.9		$	66.3

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
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, 2013				Sept. 30, 2012				Dec. 31, 2012
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	—	$	—	$	16.8	$	16.8
	Long-term investment	1	16.8		16.8		15		15		15.5		15.5
	Financial liabilities
	Checks outstanding in excess of cash balances	1	1.6		1.6		5.4		5.4		—		—
	Short-term debt	1	355		355		263		263		263		263
	Long-term debt, including current portion	2	1,097.50		1,191.10		1,057.90		1,237.50		1,140.90		1,303.10
Questar Gas [Member]	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Fair Value, by Balance Sheet Grouping	'
	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Gas's financial statements in this Quarterly Report 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, 2013				Sept. 30, 2012				Dec. 31, 2012
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	—	$	—	$	—	$	—	$	1.4	$	1.4
	Financial liabilities
	Checks outstanding in excess of cash balances	1	1.4		1.4		2		2		—		—
	Notes payable to Questar	1	195		195		206.6		206.6		166.1		166.1
	Long-term debt, including current portion	2	384.5		425.6		343		426.3		426.5		503.7
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, 2013				Sept. 30, 2012				Dec. 31, 2012
			(in millions)
	Financial assets
	Cash and cash equivalents	1	$	1.5	$	1.5	$	0.4	$	0.4	$	7.1	$	7.1
	Notes receivable from Questar	1	36.6		36.6		42		42		38.7		38.7
	Financial liabilities
	Long-term debt	2	458.8		505.5		458.9		547.8		458.9		536.6

Derivative_Instruments_and_Hed1

Derivative Instruments and Hedging Activities (Tables)	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Derivative instruments on Consolidated Statements of Income and Accumulated Other Comprehensive Income	'
	The following table presents the pre-tax effects of the derivative instruments designated as a fair value hedge (including the hedged item) and cash flow hedges on the Consolidated Statements of Income as well as the pre-tax effects of the derivative instruments designated as cash flow hedges on OCI:
			3 Months Ended						9 Months Ended						12 Months Ended
		Financial Statement Location of Gain (Loss)	September 30,						September 30,						September 30,
	Instrument and Activity		2013			2012			2013			2012			2013			2012
			(in millions)
	Fair Value Hedge
	Questar Corporation
	Interest rate derivative instrument
	Realized gain	Interest expense	$	—		$	—		$	—		$	—		$	—		$	0.7
	2.75% Notes due 2016
	Unrealized loss	Interest expense	—			—			—			—			—			(0.7		)
	Cash Flow Hedges
	Questar Pipeline
	Interest rate derivative instruments
	Deferrals of effective portions	OCI	—			—			—			—			—			(1.1		)
	Losses reclassified from AOCI into earnings for effective portions	Interest expense	(0.1		)	(0.2		)	(0.4		)	(0.4		)	(0.4		)	(0.5		)

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2013
Share-based Compensation [Abstract]	'
Transactions involving stock options under the terms of the LTSIP	'
	Stock option transactions under the terms of the LTSIP are summarized below:
		Options			Exercise						Weighted-Average Exercise Price
		Outstanding			Price Range
	Balance at December 31, 2012	770,923			$	4.37	-	$	17.35		$	11.35
	Exercised	(53,083	)		4.37		-	13.1			4.75
	Balance at September 30, 2013	717,840			$	7.84	-	$	17.35		$	11.84
Options held under the LTSIP, by exercise price range	'
	Options Outstanding													Options Exercisable
	Range of exercise							Number outstanding at Sept. 30, 2013		Weighted-average remaining term in years		Weighted-average exercise price		Number exercisable at Sept. 30, 2013	Weighted-average exercise price
	prices
	$	7.84		-	$	11.4		404,174		2.1		$	10.52	404,174	$	10.52
	13.1			-	17.35			313,666		2.8		13.54		313,666	13.54
								717,840		2.4		$	11.84	717,840	$	11.84
Transactions involving restricted shares and RSUs under the terms of the LTSIP	'
	Transactions involving RSUs under the terms of the LTSIP are summarized below:
		RSUs			Price Range						Weighted-Average Price
		Outstanding
	Granted	326,797			$	22.17	-	$	25.44		$	23.63
	Vested	(12,522	)		23.62			23.62			23.62
	Balance at September 30, 2013	314,275			$	22.17	-	$	25.44		$	23.63
	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, 2012	810,342			$	13.1	-	$	20.9		$	17.74
	Granted	658			21.53			21.53			21.53
	Vested	(417,882	)		13.1		-	20.9			17.24
	Balance at September 30, 2013	393,118			$	13.1	-	$	21.53		$	18.29
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, 2012	264,867			$	18.23	-	$	25.42		$	21.94
	Granted	126,606			39.62			39.62			39.62
	Forfeited	(3,594	)		18.23		-	39.62			33.09
	Balance at September 30, 2013	387,879			$	18.23	-	$	39.62		$	27.61

Operations_by_Line_of_Business1

Operations by Line of Business (Tables)	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Summary of continuing 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,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Revenues from Unaffiliated Customers
	Questar Gas	$	89.4		$	82.5		$	647.8		$	578.7		$	928.8		$	876.5
	Wexpro	13.2			9.8			32			27.1			41			35.5
	Questar Pipeline	47			49.5			142.3			150.1			195.3			198.7
	Total	$	149.6		$	141.8		$	822.1		$	755.9		$	1,165.10		$	1,110.70
	Revenues from Affiliated Companies
	Questar Gas	$	0.2		$	0.5		$	0.6		$	2.3		$	0.8		$	3.4
	Wexpro	68.1			69.3			215.2			204.6			284.7			271.8
	Questar Pipeline	17.6			18.4			54.8			55.2			74			73.8
	Total	$	85.9		$	88.2		$	270.6		$	262.1		$	359.5		$	349
	Operating Income (Loss)
	Questar Gas	$	(11.2	)	$	(10.7	)	$	55.3		$	52.6		$	95.6		$	90.1
	Wexpro	40.7			41			121.9			117.9			162.1			155.3
	Questar Pipeline	(52.6		)	32.6			5.7			95.2			34.5			126.2
	Corporate and other	3.7			0.7			0.3			1.4			(0.4		)	2.1
	Total	$	(19.4	)	$	63.6		$	183.2		$	267.1		$	291.8		$	373.7
	Net Income (Loss)
	Questar Gas	$	(9.0	)	$	(9.3	)	$	26.8		$	23.3		$	50.6		$	43.5
	Wexpro	27.5			26.4			82.2			76.5			109.6			100.1
	Questar Pipeline	(37.9		)	17.1			(7.6		)	49.8			7.3			67
	Corporate and other	0.2			(0.4		)	(8.3		)	(1.4		)	(10.6		)	(0.8		)
	Total	$	(19.2	)	$	33.8		$	93.1		$	148.2		$	156.9		$	209.8

Employee_Benefits_Tables

Employee Benefits (Tables)	9 Months Ended
	Sep. 30, 2013
Compensation and Retirement Disclosure [Abstract]	'
Schedule of Defined Benefit Plans Disclosures	'
	Net 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,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Service cost	$	0.2		$	0.2		$	0.6		$	0.5		$	0.8		$	0.5
	Interest cost	0.9			1			2.8			2.8			3.8			3.7
	Expected return on plan assets	(0.6		)	(0.6		)	(1.9		)	(1.7		)	(2.5		)	(2.3		)
	Amortization of transition obligation	—			0.4			—			1.2			0.4			1.8
	Recognized net actuarial loss	0.8			0.5			2.2			1.6			3.1			1.4
	Accretion of regulatory liability	0.1			0.1			0.5			0.5			0.3			0.6
	Net postretirement benefit cost	$	1.4		$	1.6		$	4.2		$	4.9		$	5.9		$	5.7
	Components of the qualified and nonqualified net pension cost included in the determination of net income (loss) are listed in the table below:
		3 Months Ended						9 Months Ended						12 Months Ended
		September 30,						September 30,						September 30,
		2013			2012			2013			2012			2013			2012
		(in millions)
	Service cost	$	3.2		$	3.2		$	10		$	9.7		$	13.5		$	12.4
	Interest cost	7.6			7.8			23.4			23.3			31.2			30.5
	Expected return on plan assets	(9.5		)	(8.0		)	(28.6		)	(23.7		)	(36.7		)	(30.8		)
	Prior service and other costs	0.2			0.4			0.8			1.1			0.8			2.1
	Recognized net actuarial loss	8			5.4			21.7			16.2			30.4			20.5
	Net pension cost	$	9.5		$	8.8		$	27.3		$	26.6		$	39.2		$	34.7

Wexpro_Acquisition_of_Producin1

Wexpro Acquisition of Producing Properties (Tables)	9 Months Ended
	Sep. 30, 2013
Wexpro Acquisition of Producing Properties [Abstract]	'
Summary information related to the Wexpro acquisition	'
	Summary information related to the Trail acquisition is shown in the table below. Amounts are provisional and are subject to post-closing adjustments.
		(in millions)
	Fair value of consideration transferred:
	Cash paid at closing	$	106.7
	Recognized amounts of identifiable assets acquired and liabilities assumed, at fair value:
	Proved properties	$	108.8
	Asset retirement obligations	(2.1		)
	Total fair value of identifiable net assets acquired	$	106.7

Nature_of_Business_Details

Nature of Business (Details)	9 Months Ended
	Sep. 30, 2013
	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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
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]	'	'	'	'	'	'
Total cost of sales	($35)	($42.10)	$157.40	$99.10	$250.60	$209.50
Questar Gas [Member]	'	'	'	'	'	'
Cost of Sales [Abstract]	'	'	'	'	'	'
Gas purchases	0.1	0	113.7	64.3	153.6	131.5
Operator service fee	68.2	69.3	215.2	204.5	284.7	271.6
Transportation and storage	18.5	19	58.6	58.5	79.7	78.6
Gathering	4.5	4.8	13.6	16	18.1	22.3
Royalties	11	7	32.4	23.4	41	34.3
Storage (injection) withdrawal, net	-37.3	-29	-18.1	-18.1	1.9	-8.8
Purchased-gas account adjustment	-15.9	-27.6	5.1	4	17.2	17.1
Other	1	1.2	3.7	3.8	4.9	5
Total Questar Gas cost of natural gas sold	50.1	44.7	424.2	356.4	601.1	551.6
Elimination of Questar Gas cost of natural gas sold - affiliated parties	-85.6	-87.5	-269.5	-259.2	-358	-344.8
Total Questar Gas cost of natural gas sold - unaffiliated parties	-35.5	-42.8	154.7	97.2	243.1	206.8
Questar Pipeline [Member]	'	'	'	'	'	'
Cost of Sales [Abstract]	'	'	'	'	'	'
Total Questar Pipeline cost of sales	$0.50	$0.70	$2.70	$1.90	$7.50	$2.70

Comprehensive_Income_Details

Comprehensive Income (Details) (USD $)	3 Months Ended			9 Months Ended			12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'	'		'	'	'
AOCI at beginning of period	($236.40)		'	($246.30)		'	($213.70)	'
OCI before reclassifications	0		'	-0.1		'	'	'
Reclassified from AOCI	9.1	[1]	'	25.1	[1]	'	'	'
Income taxes	'		'	'		'	'	'
Attributable to OCI before reclassifications	0		'	0.1		'	'	'
Attributable to amounts reclassified from AOCI	-3.4	[2]	'	-9.5	[2]	'	'	'
Total income taxes	-3.4		-2.8	-9.4		-7.9	10.8	57.7
Net other comprehensive income (loss)	5.7		4.1	15.6		12.4	-17	-93.4
AOCI at September 30, 2013	-230.7		-213.7	-230.7		-213.7	-230.7	-213.7
Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract]	'		'	'		'	'	'
Income tax benefit (expense)	10.1		-18	-59.4		-83.1	-92.8	-117.8
Pension and OPRB	'		'	'		'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'	'		'	'	'
AOCI at beginning of period	-213.5		'	-223.2		'	'	'
OCI before reclassifications	0		'	0		'	'	'
Reclassified from AOCI	9	[1]	'	24.7	[1]	'	'	'
Income taxes	'		'	'		'	'	'
Attributable to OCI before reclassifications	0		'	0		'	'	'
Attributable to amounts reclassified from AOCI	-3.4	[2]	'	-9.4	[2]	'	'	'
Total income taxes	-3.4		'	-9.4		'	'	'
Net other comprehensive income (loss)	5.6		'	15.3		'	'	'
AOCI at September 30, 2013	-207.9		'	-207.9		'	-207.9	'
Long-term invest.	'		'	'		'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'	'		'	'	'
AOCI at beginning of period	0.1		'	0.1		'	'	'
OCI before reclassifications	0		'	-0.1		'	'	'
Reclassified from AOCI	0	[1]	'	0	[1]	'	'	'
Income taxes	'		'	'		'	'	'
Attributable to OCI before reclassifications	0		'	0.1		'	'	'
Attributable to amounts reclassified from AOCI	0	[2]	'	0	[2]	'	'	'
Total income taxes	0		'	0.1		'	'	'
Net other comprehensive income (loss)	0		'	0		'	'	'
AOCI at September 30, 2013	0.1		'	0.1		'	0.1	'
Questar Pipeline [Member]	'		'	'		'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'	'		'	'	'
AOCI at beginning of period	'		'	-23.2		'	-23.2	'
Income taxes	'		'	'		'	'	'
Total income taxes	0		-0.1	-0.1		-0.2	-0.1	0.2
Net other comprehensive income (loss)	0.1		0.1	0.3		0.2	0.3	-0.4
AOCI at September 30, 2013	-22.9		-23.2	-22.9		-23.2	-22.9	-23.2
Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract]	'		'	'		'	'	'
Income tax benefit (expense)	19.7		-9.9	2.2		-28.7	-6.4	-38.1
Questar Pipeline [Member] | Interest rate cash flow hedges	'		'	'		'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'		'	'		'	'	'
AOCI at beginning of period	-23		'	-23.2		'	'	'
OCI before reclassifications	0		'	0		'	'	'
Reclassified from AOCI	0.1	[1]	'	0.4	[1]	'	'	'
Income taxes	'		'	'		'	'	'
Attributable to OCI before reclassifications	0		'	0		'	'	'
Attributable to amounts reclassified from AOCI	0	[2]	'	-0.1	[2]	'	'	'
Total income taxes	0		'	-0.1		'	'	'
Net other comprehensive income (loss)	0.1		'	0.3		'	'	'
AOCI at September 30, 2013	-22.9		'	-22.9		'	-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		'	-0.4		'	'	'
Income tax benefit (expense)	$0		'	$0.10		'	'	'
[1]	Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income.
[2]	Interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income.

Earnings_Per_Share_Details

Earnings Per Share (Details)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]	'	'	'	'	'	'
Weighted-average basic common shares outstanding (in shares)	175.5	175.4	175.4	177	175.5	177.2
Potential number of shares issuable under the Company's LTSIP (in shares)	0	1.1	0.7	1.1	0.6	1.1
Weighted-average diluted common shares outstanding (in shares)	175.5	176.5	176.1	178.1	176.1	178.3

Asset_Retirement_Obligations_D

Asset Retirement Obligations (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
AROs at beginning of year	$67.20	$63.80
Accretion	2.4	2.3
Liabilities incurred	4.2	2.2
Revisions in estimated cash flows	-6.8	-1.2
Liabilities settled	-1.1	-0.8
AROs at September 30,	$65.90	$66.30

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Millions, unless otherwise specified
Carrying Amount [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	$0	$16.80	$0
Long-term investment	16.8	15.5	15
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	1.6	0	5.4
Short-term debt	355	263	263
Long-term debt, including current portion	1,097.50	1,140.90	1,057.90
Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	0	16.8	0
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	1.6	0	5.4
Short-term debt	355	263	263
Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]	'	'	'
Financial liabilities [Abstract]	'	'	'
Long-term debt, including current portion	1,191.10	1,303.10	1,237.50
Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Long-term investment	16.8	15.5	15
Questar Gas [Member] | Carrying Amount [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	0	1.4	0
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	1.4	0	2
Notes payable to Questar	195	166.1	206.6
Long-term debt, including current portion	384.5	426.5	343
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	0	1.4	0
Financial liabilities [Abstract]	'	'	'
Checks outstanding in excess of cash balances	1.4	0	2
Notes payable to Questar	195	166.1	206.6
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]	'	'	'
Financial liabilities [Abstract]	'	'	'
Long-term debt, including current portion	425.6	503.7	426.3
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	1.5	7.1	0.4
Notes receivable from Questar	36.6	38.7	42
Financial liabilities [Abstract]	'	'	'
Long-term debt, including current portion	458.8	458.9	458.9
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]	'	'	'
Financial assets [Abstract]	'	'	'
Cash and cash equivalents	1.5	7.1	0.4
Notes receivable from Questar	36.6	38.7	42
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]	'	'	'
Financial liabilities [Abstract]	'	'	'
Long-term debt, including current portion	$505.50	$536.60	$547.80

Derivative_Instruments_and_Hed2

Derivative Instruments and Hedging Activities Effects on Statements of Income and OCI (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Fair Value Hedging [Member] | Interest Rate Derivative Instruments [Member] | Interest Expense [Member]	'	'	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'	'	'
Realized gain	$0	$0	$0	$0	$0	$0.70
Fair Value Hedging [Member] | Notes Due 2016, 2.75% [Member] | Interest Expense [Member]	'	'	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'	'	'
Unrealized loss	0	0	0	0	0	-0.7
Questar Pipeline [Member] | Cash Flow Hedging [Member] | Interest Rate Derivative Instruments [Member] | Other Comprehensive Income [Member]	'	'	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'	'	'
Deferrals of effective portions	0	0	0	0	0	-1.1
Questar Pipeline [Member] | Cash Flow Hedging [Member] | Interest Rate Derivative Instruments [Member] | Interest Expense [Member]	'	'	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'	'	'
Losses reclassified from AOCI into earnings for effective portions	($0.10)	($0.20)	($0.40)	($0.40)	($0.40)	($0.50)

Derivative_Instruments_and_Hed3

Derivative Instruments and Hedging Activities Additional Information (Details) (USD $)

3 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2011

Mar. 31, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Jun. 30, 2011

Cash Flow Hedging [Member]

Cash Flow Hedging [Member]

Cash Flow Hedging [Member]

Cash Flow Hedging [Member]

Cash Flow Hedging [Member]

Cash Flow Hedging [Member]

Cash Flow Hedging [Member]

Fair Value Hedging [Member]

Fair Value Hedging [Member]

Fair Value Hedging [Member]

Fair Value Hedging [Member]

Fair Value Hedging [Member]

Fair Value Hedging [Member]

Fair Value Hedging [Member]

Fair Value Hedging [Member]

Questar Pipeline [Member]

Questar Pipeline [Member]

Questar Pipeline [Member]

Questar Pipeline [Member]

Questar Pipeline [Member]

Questar Pipeline [Member]

Questar Pipeline [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]

Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]

Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]

Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]

Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]

Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]

Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]

Derivative [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Notional amount

'

'

'

'

'

'

$150,000,000

'

'

'

'

'

'

'

$125,000,000

Weighted-average fixed interest rate (in hundredths)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.75%

Derivative, gain on derivative

'

'

'

'

'

'

'

7,200,000

'

'

'

'

'

'

'

Debt Instrument, Face Amount

'

'

'

'

'

'

180,000,000

'

'

'

'

'

'

'

'

Interest payment for terminated derivative instrument

'

'

'

'

'

'

37,300,000

'

'

'

'

'

'

'

'

Life of long-term debt associated with cash flow hedges

'

'

'

'

'

'

'30 years

'

'

'

'

'

'

'

'

Ineffectiveness recognized on the fair value hedge

'

'

'

'

'

'

'

'

0

0

0

0

0

0

'

Ineffectiveness recognized on cash flow hedges

0

0

0

0

0

'

'

'

'

'

'

'

'

'

'

Interest Rate Cash Flow Hedge Ineffectiveness is Immaterial

'

'

'

'

'

'Ineffectiveness recognized on the cash flow hedges was de minimis

'

'

'

'

'

'

'

'

'

Pre-tax net losses expected to be reclassified from AOCI to Consolidated statement of income

'

'

$500,000

'

'

'

'

'

'

'

'

'

'

'

'

Reclassification from accumulated OCI to income, estimated 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, 2013	Sep. 30, 2012
Share-based Compensation [Abstract]	'	'
Share-based compensation	$7.70	$7.50
Deferred share-based compensation on restricted share awards and restricted stock unit awards	6.5	'
Cash flow from income tax benefits in excess of recognized compensation expense	$1.50	$8.10
Shares available for future grant (in shares)	5,577,106	'

ShareBased_Compensation_Stock_

Share-Based Compensation Stock options (Details) (Stock Options [Member], USD $)	9 Months Ended
	Sep. 30, 2013
Stock option transactions under the terms of the LTSIP - shares [Roll Forward]	'
Balance at December 31, 2012	770,923
Granted	0
Exercised	-53,083
Balance at September 30, 2013	717,840
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at December 31, 2012	$11.35
Exercised	$4.75
Balance at September 30, 2013	$11.84
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]	'
Options Outstanding, Number outstanding at end of period	717,840
Options Outstanding, Weighted-average remaining term (in years and months)	'2 years 5 months
Options Exercisable, Number exercisable at end of period	717,840
Options Exercisable, Weighted-average exercise price	$11.84
Stock options, additional disclosures [Abstract]	'
Unvested stock options decrease in period (in shares)	29,398
Number of unvested options at end of period (in shares)	0
$7.84 - $11.40 [Member]	'
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at September 30, 2013	$10.52
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	404,174
Options Outstanding, Weighted-average remaining term (in years and months)	'2 years 1 month
Options Exercisable, Number exercisable at end of period	404,174
Options Exercisable, Weighted-average exercise price	$10.52
$13.10 - $17.35 [Member]	'
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at September 30, 2013	$13.54
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	313,666
Options Outstanding, Weighted-average remaining term (in years and months)	'2 years 9 months
Options Exercisable, Number exercisable at end of period	313,666
Options Exercisable, Weighted-average exercise price	$13.54
Minimum [Member]	'
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at December 31, 2012	$4.37
Exercised	$4.37
Balance at September 30, 2013	$7.84
Maximum [Member]	'
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]	'
Balance at December 31, 2012	$17.35
Exercised	$13.10
Balance at September 30, 2013	$17.35

ShareBased_Compensation_Restri

Share-Based Compensation Restricted shares (Details) (Restricted Shares [Member], USD $)	9 Months Ended
	Sep. 30, 2013
Transactions under the terms of the LTSIP - shares [Roll Forward]	'
Balance at December 31, 2012	810,342
Granted	658
Vested	-417,882
Balance at September 30, 2013	393,118
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2012	$17.74
Granted	$21.53
Vested	$17.24
Balance at September 30, 2013	$18.29
Share-based awards other than options, additional disclosures [Abstract]	'
Weighted-average remaining vesting period of share-based awards (in months)	'11 months
Minimum [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2012	$13.10
Granted	$21.53
Vested	$13.10
Balance at September 30, 2013	$13.10
Share-based awards other than options, additional disclosures [Abstract]	'
Vesting period for share-based award (in years)	'3 years
Maximum [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Balance at December 31, 2012	$20.90
Granted	$21.53
Vested	$20.90
Balance at September 30, 2013	$21.53
Share-based awards other than options, additional disclosures [Abstract]	'
Vesting period for share-based award (in years)	'4 years

ShareBased_Compensation_Restri1

Share-Based Compensation Restricted stock units (Details) (USD $)	9 Months Ended
	Sep. 30, 2013
Restricted Stock Units (RSUs) [Member]	'
Transactions under the terms of the LTSIP - shares [Roll Forward]	'
Granted	326,797
Vested	-12,522
Balance at September 30, 2013	314,275
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Granted	$23.63
Vested	$23.62
Balance at September 30, 2013	$23.63
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)	'17 months
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Deferred Restricted Stock Units (RSUs) [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Granted	$15.67
Share-based awards other than options, additional disclosures [Abstract]	'
Vesting period for share-based award (in years)	'3 years
Number of deferred restricted stock units issued (in shares)	73,071
Number of shares of common stock to be issued for each vested restricted stock unit (RSU)	1
Minimum [Member] | Restricted Stock Units (RSUs) [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Granted	$22.17
Vested	$23.62
Balance at September 30, 2013	$22.17
Maximum [Member] | Restricted Stock Units (RSUs) [Member]	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'
Granted	$25.44
Vested	$23.62
Balance at September 30, 2013	$25.44

ShareBased_Compensation_Perfor

Share-Based Compensation Performance shares (Details) (Performance Shares [Member], USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Transactions under the terms of the LTSIP - shares [Roll Forward]	'	'
Balance at December 31, 2012	264,867	'
Granted	126,606	'
Forfeited	-3,594	'
Balance at September 30, 2013	387,879	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'	'
Balance at December 31, 2012	$21.94	'
Granted	$39.62	'
Forfeited	$33.09	'
Balance at September 30, 2013	$27.61	'
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	$1.20	$1.40
Weighted-average remaining vesting period of share-based awards (in months)	'15 months	'
Vested Undistributed [Member]	'	'
Transactions under the terms of the LTSIP - shares [Roll Forward]	'	'
Balance at September 30, 2013	5,330	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'	'
Balance at September 30, 2013	$23.39	'
Minimum [Member]	'	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'	'
Balance at December 31, 2012	$18.23	'
Granted	$39.62	'
Forfeited	$18.23	'
Balance at September 30, 2013	$18.23	'
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 2014	'
Maximum [Member]	'	'
Transactions under the terms of LTSIP - grant-date fair value [Roll Forward]	'	'
Balance at December 31, 2012	$25.42	'
Granted	$39.62	'
Forfeited	$39.62	'
Balance at September 30, 2013	$39.62	'
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 2016	'

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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
			lines_of_business
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Number of principal complementary lines of business	'	'	3	'	'	'
Revenues from Unaffiliated Customers	$149.60	$141.80	$822.10	$755.90	$1,165.10	$1,110.70
Operating Income (Loss)	-19.4	63.6	183.2	267.1	291.8	373.7
Net Income (Loss)	-19.2	33.8	93.1	148.2	156.9	209.8
Questar Gas [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues from Unaffiliated Customers	89.4	82.5	647.8	578.7	928.8	876.5
Operating Income (Loss)	-11.2	-10.7	55.3	52.6	95.6	90.1
Net Income (Loss)	-9	-9.3	26.8	23.3	50.6	43.5
Wexpro [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues from Unaffiliated Customers	13.2	9.8	32	27.1	41	35.5
Operating Income (Loss)	40.7	41	121.9	117.9	162.1	155.3
Net Income (Loss)	27.5	26.4	82.2	76.5	109.6	100.1
Questar Pipeline [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues from Unaffiliated Customers	47	49.5	142.3	150.1	195.3	198.7
Operating Income (Loss)	-52.6	32.6	5.7	95.2	34.5	126.2
Net Income (Loss)	-37.9	17.1	-7.6	49.8	7.3	67
Questar Corp and Other [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Operating Income (Loss)	3.7	0.7	0.3	1.4	-0.4	2.1
Net Income (Loss)	0.2	-0.4	-8.3	-1.4	-10.6	-0.8
Intersegment Eliminations [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues from Unaffiliated Customers	85.9	88.2	270.6	262.1	359.5	349
Intersegment Eliminations [Member] | Questar Gas [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues from Unaffiliated Customers	0.2	0.5	0.6	2.3	0.8	3.4
Intersegment Eliminations [Member] | Wexpro [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues from Unaffiliated Customers	68.1	69.3	215.2	204.6	284.7	271.8
Intersegment Eliminations [Member] | Questar Pipeline [Member]	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'
Revenues from Unaffiliated Customers	$17.60	$18.40	$54.80	$55.20	$74	$73.80

Employee_Benefits_Details

Employee Benefits (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Qualified and nonqualified pension plans [Member]	'	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'	'
Service cost	$3.20	$3.20	$10	$9.70	$13.50	$12.40
Interest cost	7.6	7.8	23.4	23.3	31.2	30.5
Expected return on plan assets	-9.5	-8	-28.6	-23.7	-36.7	-30.8
Prior service and other costs	0.2	0.4	0.8	1.1	0.8	2.1
Recognized net actuarial loss	8	5.4	21.7	16.2	30.4	20.5
Net benefit cost	9.5	8.8	27.3	26.6	39.2	34.7
Estimated qualified pension plan cost for current fiscal year	32	'	32	'	32	'
Estimated nonqualified pension plan cost for current fiscal year	4.3	'	4.3	'	4.3	'
Postretirement benefits plan [Member]	'	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'	'
Service cost	0.2	0.2	0.6	0.5	0.8	0.5
Interest cost	0.9	1	2.8	2.8	3.8	3.7
Expected return on plan assets	-0.6	-0.6	-1.9	-1.7	-2.5	-2.3
Amortization of transition obligation	0	0.4	0	1.2	0.4	1.8
Recognized net actuarial loss	0.8	0.5	2.2	1.6	3.1	1.4
Accretion of regulatory liability	0.1	0.1	0.5	0.5	0.3	0.6
Net benefit cost	1.4	1.6	4.2	4.9	5.9	5.7
Estimated postretirement benefits cost for current fiscal year, before accretion of regulatory liability	$5	'	$5	'	$5	'

Debt_Details

Debt (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013
				Revolving credit facility [Member]	Revolving credit facility [Member]	Commercial paper [Member]	Commercial paper [Member]	Commercial paper [Member]	Questar Gas [Member]	Questar Gas [Member]	Questar Gas [Member]
									4.78% and 4.83% Notes due 2043 and 2048 [Member]	4.78% Notes due 2043 [Member]	4.83% Notes due 2048 [Member]
Short-term Debt [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Line of Credit Facility, Maximum Borrowing Capacity	'	'	'	$500,000,000	$750,000,000	'	'	'	'	'	'
Debt Instrument Maturity Dates	'	'	'	'8/31/2016	'4/19/2018	'	'	'	'	'	'
Consolidated Funded Debt Percentage Of Consolidated Capital Permitted Under Credit Arrangement Amendment	'	'	'	'	70.00%	'	'	'	'	'	'
Amounts borrowed under short-term financing arrangements	355,000,000	263,000,000	263,000,000	'	0	355,000,000	263,000,000	263,000,000	'	'	'
Questar Gas Long-term Debt Commitment [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Debt Instrument, Face Amount	'	'	'	'	'	'	'	'	$150,000,000	$90,000,000	$60,000,000
Funding Date of Long-term Debt	'	'	'	'	'	'	'	'	'December 2013	'	'
Long-term Debt, Life (in years)	'	'	'	'	'	'	'	'	'	'30 years	'35 years
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)	'	'	'	'	'	'	'	'	'	4.78%	4.83%

Strategic_Review_of_Questar_So1

Strategic Review of Questar Southern Trails Pipeline and Impairment of Eastern Segment (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Property, Plant and Equipment [Line Items]	'	'	'	'	'	'	'
Net book value of Questar Southern Trails Pipeline	$3,495	$3,261.20	$3,495	$3,261.20	$3,495	$3,261.20	$3,317
Pre-tax asset impairment charge	80.6	0	80.6	0	80.6	0	'
Questar Pipeline [Member]	'	'	'	'	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'	'	'	'	'
Net book value of Questar Southern Trails Pipeline	1,148.30	1,203.20	1,148.30	1,203.20	1,148.30	1,203.20	1,210.80
Pre-tax asset impairment charge	80.6	0	80.6	0	80.6	0	'
Questar Pipeline [Member] | Questar Southern Trails Pipeline - Western Segment [Member]	'	'	'	'	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'	'	'	'	'
Net book value of Questar Southern Trails Pipeline	21	'	21	'	21	'	'
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_Producin2

Wexpro Acquisition of Producing Properties (Details) (USD $)	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2013
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	'
Business Combination, Consideration Transferred [Abstract]	'	'
Cash paid at closing	$106.70	'
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]	'	'
Proved properties	108.8	108.8
Asset retirement obligations	-2.1	-2.1
Total fair value of identifiable net assets acquired	106.7	106.7
Business Acquisition, Income Information [Abstract]	'	'
Revenue of Acquiree since Acquisition Date, Actual	1.5	'
Earnings or Loss of Acquiree since Acquisition Date, Actual	0.3	'
Business Combination, Separately recognized Transactions, Additional Disclosures [Abstract]	'	'
Acquisition Cost Expensed	'	$0.20
Acquisition Cost Expensed, Financial Statement Caption	'	'general and administrative expense