Dominion Questar 10-Q 28 Apr 16 2016 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	3 Months Ended
	Mar. 31, 2016shares
Entity Information [Line Items]
Entity Registrant Name	QUESTAR CORP
Entity Central Index Key	751,652
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	175,397,041
Questar Gas [Member]
Entity Information [Line Items]
Entity Registrant Name	QUESTAR GAS CO
Entity Central Index Key	68,589
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	9,189,626
Questar Pipeline [Member]
Entity Information [Line Items]
Entity Registrant Name	QUESTAR PIPELINE CO
Entity Central Index Key	764,044
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	6,550,843

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
REVENUES
Questar Gas / Revenues	$ 407.9	$ 374.8	$ 950.7	$ 939.4
Wexpro	3.5	6.3	20.1	29.6
Questar Pipeline / Revenues from unaffiliated customers	43	46.8	184.1	189
Other	1.9	0.7	7.7	3
Total Revenues	456.3	428.6	1,162.6	1,161
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	158.5	131.8	201.9	169.9
Operating and maintenance	50.4	52.3	179.7	189.6
General and administrative	29.6	29.4	109.2	121.8
Pension settlement costs	0	0	16.7	0
Merger and restructuring costs	14.6	0	14.6	0
Production and other taxes	11.7	13.8	49.2	62.1
Depreciation, depletion and amortization	55.9	54.3	217.6	212.7
Abandonment and impairment	0.2	0	12.7	2
Total Operating Expenses	320.9	281.6	801.6	758.1
Net gain (loss) from asset sales	0.3	0	2.1	1.2
OPERATING INCOME	135.7	147	363.1	404.1
Interest and other income	1	1.4	3.8	6.2
Income from unconsolidated affiliate	1	0.9	3.8	3.5
Interest expense	(15.8)	(15.9)	(62.9)	(63.2)
INCOME BEFORE INCOME TAXES	121.9	133.4	307.8	350.6
Income taxes	(43.4)	(48.8)	(105.2)	(124.6)
NET INCOME	$ 78.5	$ 84.6	$ 202.6	$ 226
Earnings Per Common Share
Basic (usd per share)	$ 0.45	$ 0.48	$ 1.15	$ 1.29
Diluted (usd per share)	$ 0.45	$ 0.48	$ 1.15	$ 1.28
Weighted-average common shares outstanding
Used in basic calculation (in shares)	175.8	176.2	175.9	176
Used in diluted calculation (in shares)	176.1	176.5	176.1	176.3
Dividends per common share (usd per share)	$ 0.22	$ 0.21	$ 0.85	$ 0.78
Questar Gas [Member]
REVENUES
Total Revenues	$ 407.9	$ 374.8	$ 950.7	$ 939.4
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	256.9	233.6	581.4	583.8
Operating and maintenance	34.6	33.1	113.4	115.8
General and administrative	13	13.4	50.2	52.4
Depreciation and amortization	14.7	13.5	56.3	53.9
Other taxes	5.3	4.6	20	17.3
Total Operating Expenses	324.5	298.2	821.3	823.2
Net gain (loss) from asset sales	0	0	0	0.1
OPERATING INCOME	83.4	76.6	129.4	116.3
Interest and other income	1	1.1	4.7	5.7
Interest expense	(7.7)	(7.1)	(28.9)	(28.2)
INCOME BEFORE INCOME TAXES	76.7	70.6	105.2	93.8
Income taxes	(29.1)	(26.8)	(37.1)	(34.4)
NET INCOME	47.6	43.8	68.1	59.4
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	43	46.8	184.1	189
Revenues from affiliated companies	19.3	19.4	75	73.8
Total Revenues	62.3	66.2	259.1	262.8
OPERATING EXPENSES
Operating and maintenance	8.6	10.1	36.1	40.1
General and administrative	10.3	10.5	38.7	39.1
Depreciation and amortization	13.7	14	54.3	54.9
Other taxes	2.3	2.3	8.8	9.1
Cost of sales (excluding operating expenses shown separately)	0.1	1.9	7.1	4.2
Total Operating Expenses	35	38.8	145	147.4
Net gain (loss) from asset sales	0.3	0	0.5	(0.5)
OPERATING INCOME	27.6	27.4	114.6	114.9
Interest and other income	0.1	0.2	0.8	1.1
Income from unconsolidated affiliate	1	0.9	3.8	3.5
Interest expense	(6.2)	(6.6)	(25.6)	(26.2)
INCOME BEFORE INCOME TAXES	22.5	21.9	93.6	93.3
Income taxes	(8.3)	(8)	(33.7)	(34.5)
NET INCOME	$ 14.2	$ 13.9	$ 59.9	$ 58.8

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Net income	$ 78.5	$ 84.6	$ 202.6	$ 226
Other comprehensive income (loss):
Pension and other postretirement benefits	4	6	23.6	(95.2)
Interest rate cash flow hedge amortization	0.2	0.2	0.6	0.5
Commodity cash flow hedge	(0.2)	0	(0.4)	0
Income taxes	(1.6)	(2.4)	(9.2)	36.3
Net other comprehensive income (loss)	2.4	3.8	14.6	(58.4)
COMPREHENSIVE INCOME	80.9	88.4	217.2	167.6
Questar Pipeline [Member]
Net income	14.2	13.9	59.9	58.8
Other comprehensive income (loss):
Interest rate cash flow hedge amortization	0.2	0.2	0.6	0.5
Commodity cash flow hedge	(0.2)	0	(0.4)	0
Income taxes	(0.1)	(0.1)	(0.2)	(0.1)
Net other comprehensive income (loss)	(0.1)	0.1	0	0.4
COMPREHENSIVE INCOME	$ 14.1	$ 14	$ 59.9	$ 59.2

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Current Assets
Cash and cash equivalents	$ 0.4	$ 25	$ 4.8
Accounts receivable, net	107.1	168	104.5
Unbilled gas accounts receivable	58.7	91.3	41.5
Gas stored underground	9.6	45.1	12.4
Materials and supplies	30.1	28.4	28.7
Current regulatory assets	20.3	70	43
Prepaid expenses and other	8.4	12.3	8.7
Total Current Assets	234.6	440.1	243.6
Property, Plant and Equipment	6,240.9	6,182	6,033.1
Accumulated depreciation, depletion and amortization	(2,380.4)	(2,333.3)	(2,277.2)
Net Property, Plant and Equipment	3,860.5	3,848.7	3,755.9
Investment in unconsolidated affiliate	23.7	23.9	24.5
Noncurrent regulatory assets	14.4	9.3	17.3
Other noncurrent assets	46	44.2	43.4
TOTAL ASSETS	4,179.2	4,366.2	4,084.7
Current Liabilities
Short-term debt	458.5	457.6	214
Accounts payable and accrued expenses	177.2	224.8	200.5
Current regulatory liabilities	63.6	6.4	5.2
Current portion of long-term debt and capital lease obligation	1.2	251.3	277.4
Total Current Liabilities	700.5	940.1	697.1
Long-term debt and capital lease obligation, less current portion	992.7	992.6	992.5
Deferred income taxes	776	779.5	708.4
Asset retirement obligations	70.5	67.6	75
Defined benefit pension plan and other postretirement benefits	117.3	123	155.7
Noncurrent regulatory liabilities	82.1	75.6	72.5
Customer contributions in aid of construction	23.4	23.7	28
Other noncurrent liabilities	56	49	57.2
COMMON SHAREHOLDERS' EQUITY
Common stock	472.4	469	477.6
Retained earnings	1,071.2	1,031.4	1,018.2
Accumulated other comprehensive (loss)	(182.9)	(185.3)	(197.5)
Total Common Shareholders' Equity	1,360.7	1,315.1	1,298.3
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	4,179.2	4,366.2	4,084.7
Questar Gas [Member]
Current Assets
Cash and cash equivalents	0	10.5	0
Accounts receivable, net	97.3	112	81.2
Unbilled gas accounts receivable	58.7	91	41.5
Accounts receivable from affiliates	71.5	69.2	56.3
Gas stored underground	7.1	43.9	9.5
Materials and supplies	18.8	17.1	17.3
Current regulatory assets	20.2	69.8	42.1
Prepaid expenses and other	2.9	3.5	2.4
Total Current Assets	276.5	417	250.3
Property, Plant and Equipment	2,618.8	2,570.3	2,400.7
Accumulated depreciation, depletion and amortization	(820.3)	(812.2)	(791.5)
Net Property, Plant and Equipment	1,798.5	1,758.1	1,609.2
Noncurrent regulatory assets	13.5	8.1	16.1
Other noncurrent assets	5.6	5.7	5.7
TOTAL ASSETS	2,094.1	2,188.9	1,881.3
Current Liabilities
Checks outstanding in excess of cash balances	0.7	0	0.4
Notes payable to Questar	140.5	273.3	35.8
Accounts payable and accrued expenses	79.7	122.5	126
Accounts payable to affiliates	75.3	74.5	71.4
Customer advances	9.8	34.3	9.5
Current regulatory liabilities	61.8	4	4.3
Total Current Liabilities	367.8	508.6	247.4
Long-term debt, less current portion	527.6	527.4	526.8
Deferred income taxes	438.4	436.7	381.4
Noncurrent regulatory liabilities	71.9	65.6	63.3
Customer contributions in aid of construction	23.4	23.7	28
Other noncurrent liabilities	2.3	2.2	2.8
COMMON SHAREHOLDERS' EQUITY
Common stock	23	23	23
Additional paid-in capital	267.2	266.8	265.7
Retained earnings	372.5	334.9	342.9
Total Common Shareholders' Equity	662.7	624.7	631.6
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	2,094.1	2,188.9	1,881.3
Questar Pipeline [Member]
Current Assets
Cash and cash equivalents	1.2	10.2	6.1
Notes receivable from Questar	33.2	6	35.9
Accounts receivable, net	17.2	29.6	16.8
Accounts receivable from affiliates	50.4	49.8	44.3
Gas stored underground	2.5	1.2	2.9
Materials and supplies	6.3	6.7	7.1
Current regulatory assets	0.1	0.2	0.9
Prepaid expenses and other	2.7	4.4	3.6
Total Current Assets	113.6	108.1	117.6
Property, Plant and Equipment	1,857.1	1,851.1	1,837.5
Accumulated depreciation, depletion and amortization	(722.8)	(709.7)	(687.9)
Net Property, Plant and Equipment	1,134.3	1,141.4	1,149.6
Investment in unconsolidated affiliate	23.7	23.9	24.5
Noncurrent regulatory and other assets	5.1	5.3	5.5
TOTAL ASSETS	1,276.7	1,278.7	1,297.2
Current Liabilities
Accounts payable and accrued expenses	20.7	16.1	33.9
Accounts payable to affiliates	8.6	15.8	3.4
Current regulatory liabilities	1.8	2.4	0.9
Current portion of long-term debt	0	0	25.1
Total Current Liabilities	31.1	34.3	63.3
Long-term debt, less current portion	429.4	429.2	428.8
Deferred income taxes	251.2	249.9	239.4
Noncurrent regulatory and other liabilities	17.4	16.3	16
COMMON SHAREHOLDERS' EQUITY
Common stock	6.6	6.6	6.6
Additional paid-in capital	353.9	353.4	351.9
Retained earnings	209.5	211.3	213.6
Accumulated other comprehensive (loss)	(22.4)	(22.3)	(22.4)
Total Common Shareholders' Equity	547.6	549	549.7
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	$ 1,276.7	$ 1,278.7	$ 1,297.2

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
OPERATING ACTIVITIES
Net income	$ 78.5	$ 84.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	58.4	56.2
Deferred income taxes	(5.1)	(3.8)
Abandonment and impairment	0.2	0
Share-based compensation	2.7	3.2
Net (gain) from asset sales	(0.3)	0
(Income) from unconsolidated affiliate	(1)	(0.9)
Distributions from unconsolidated affiliate and other	1.5	1.5
Changes in operating assets and liabilities	198.1	82.6
NET CASH PROVIDED BY OPERATING ACTIVITIES	333	223.4
INVESTING ACTIVITIES
Property, plant and equipment purchased	(68.5)	(66.1)
Questar Gas acquisition of gas distribution system	0	(11.4)
Cash used in disposition of assets	(0.9)	(0.6)
Proceeds from disposition of assets	0.3	0.2
NET CASH USED IN INVESTING ACTIVITIES	(69.1)	(77.9)
FINANCING ACTIVITIES
Common stock issued	3.5	1.3
Common stock repurchased	(2.8)	(3.6)
Change in short-term debt	0.9	(133)
Long-term debt repaid	(250)	0
Capital lease obligation repaid	(0.3)	(0.3)
Revolver issuance costs paid	(1.2)	0
Dividends paid	(38.7)	(37.1)
Tax benefits from share-based compensation	0.1	0
NET CASH USED IN FINANCING ACTIVITIES	(288.5)	(172.7)
Change in cash and cash equivalents	(24.6)	(27.2)
Beginning cash and cash equivalents	25	32
Ending cash and cash equivalents	0.4	4.8
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	47.6	43.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	16.1	14.9
Deferred income taxes	1.7	(2.4)
Share-based compensation	0.4	0.3
Net (gain) from asset sales	0	0
Changes in operating assets and liabilities	125.5	80
NET CASH PROVIDED BY OPERATING ACTIVITIES	191.3	136.6
INVESTING ACTIVITIES
Property, plant and equipment purchased	(59.1)	(43)
Questar Gas acquisition of gas distribution system	0	(11.4)
Cash used in disposition of assets	(0.7)	(0.5)
Proceeds from disposition of assets	0.1	0.1
NET CASH USED IN INVESTING ACTIVITIES	(59.7)	(54.8)
FINANCING ACTIVITIES
Change in notes payable to Questar	(132.8)	(83.5)
Checks outstanding in excess of cash balances	0.7	0.4
Dividends paid to Questar	(10)	(18.5)
NET CASH USED IN FINANCING ACTIVITIES	(142.1)	(101.6)
Change in cash and cash equivalents	(10.5)	(19.8)
Beginning cash and cash equivalents	10.5	19.8
Ending cash and cash equivalents	0	0
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	14.2	13.9
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.3	14.5
Deferred income taxes	1.2	(0.2)
Share-based compensation	0.5	0.5
Net (gain) from asset sales	(0.3)	0
(Income) from unconsolidated affiliate	(1)	(0.9)
Distributions from unconsolidated affiliate and other	1.4	1.3
Changes in operating assets and liabilities	10.5	6.2
NET CASH PROVIDED BY OPERATING ACTIVITIES	40.8	35.3
INVESTING ACTIVITIES
Property, plant and equipment purchased	(6.6)	(8.7)
Cash used in disposition of assets	(0.2)	(0.1)
Proceeds from disposition of assets	0.2	0
NET CASH USED IN INVESTING ACTIVITIES	(6.6)	(8.8)
FINANCING ACTIVITIES
Change in notes receivable from Questar	(27.2)	4.2
Dividends paid to Questar	(16)	(32)
NET CASH USED IN FINANCING ACTIVITIES	(43.2)	(27.8)
Change in cash and cash equivalents	(9)	(1.3)
Beginning cash and cash equivalents	10.2	7.4
Ending cash and cash equivalents	$ 1.2	$ 6.1

Nature of Business

Nature of Business	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business Questar Corporation (the Company) 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).

Proposed Merger with Dominion R

Proposed Merger with Dominion Resources	3 Months Ended
	Mar. 31, 2016
Business Combinations [Abstract]
Proposed Merger with Dominion	Proposed Merger with Dominion Resources On January 31, 2016 , the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”), by and among the Company, Dominion Resources, Inc., a Virginia corporation (“Parent”) and Diamond Beehive Corp., a Utah corporation and a direct wholly-owned subsidiary of Parent (“Merger Sub”). The Merger Agreement provides for the merger of Merger Sub with and into the Company on the terms and subject to the conditions set forth in the Merger Agreement (the “Merger”), with the Company continuing as the surviving corporation in the Merger and becoming a direct, wholly-owned subsidiary of Parent. At the effective time of the Merger (the “Effective Time”), by virtue of the Merger and without any action on the part of the Company, Parent or Merger Sub or any holder of any shares of common stock, no par value per share, of the Company (the “Company Common Stock”) or any shares of capital stock of Merger Sub, each share of the Company Common Stock issued and outstanding immediately prior to the Effective Time (other than Dissenting Shares and shares of Company Common Stock that are owned by Parent or Merger Sub or any of their respective subsidiaries, in each case immediately prior to the Effective Time) will be converted automatically into the right to receive $25.00 in cash, without interest. Closing of the Merger is subject to the satisfaction or waiver of specified closing conditions, including (i) the approval of the Merger by the holders of a majority of the outstanding shares of Company Common Stock, (ii) the receipt of regulatory approvals required to close the Merger, including approvals from the Public Service Commission of Utah (if required) and the Public Service Commission of Wyoming, (iii) the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, (iv) the absence of any law, statute, ordinance, code, rule, regulation, ruling, decree, judgment, injunction or order of a governmental authority that prohibits the consummation of the Merger, and (v) other customary closing conditions, including (a) the accuracy of each party’s representations and warranties (subject to customary materiality qualifiers), (b) each party’s compliance in all material respects with its obligations and covenants contained in the Merger Agreement, and (c) the absence of a material adverse effect on the Company. In addition, the obligations of Parent and Merger Sub to consummate the Merger are subject to the required regulatory approvals not imposing or requiring any undertakings, terms, conditions, liabilities, obligations, commitments or sanctions, or any structural or remedial actions that constitute a Company Material Adverse Effect. On February 23, 2016, the Federal Trade Commission granted early termination of the 30-day waiting period under the federal Hart-Scott-Rodino Antitrust Improvements Act with regards to the Merger. On March 3, 2016, Questar and Parent jointly filed merger applications with the Public Service Commission of Utah and the Wyoming Public Service Commission and provided notice of the proposed Merger to the Idaho Public Utilities Commission. Hearings are scheduled in Utah and Wyoming during the third quarter. A shareholder vote on the Merger is scheduled for May 12, 2016. The Merger Agreement also contains customary representations, warranties and covenants of both the Company and Parent. These covenants include, among others, an obligation on behalf of the Company to use reasonable best efforts to conduct its business in all material respects in the ordinary course until the Merger is consummated, subject to certain exceptions. The Company has made certain additional customary covenants, including, among others, subject to certain exceptions, (a) causing a meeting of the Company’s shareholders to be held to consider approval of the Merger Agreement, and (b) a customary non-solicitation covenant prohibiting the Company from soliciting, providing non-public information or entering into discussions or negotiations concerning proposals relating to alternative business combination transactions, except as permitted under the Merger Agreement. In addition, the parties are required to use reasonable best efforts to obtain any required regulatory approvals. The Merger Agreement may be terminated by each of the Company and Parent under certain circumstances, including if the Merger is not consummated by February 28, 2017 (subject to certain extension rights, up to a maximum of nine months , as specified in the Merger Agreement). The Merger Agreement contains certain termination rights for both Parent and the Company, and provides that, upon termination of the Merger Agreement under specified circumstances, Parent would be required to pay a termination fee of $154 million to the Company (the “Parent Termination Fee”) and the Company would be required to pay Parent a termination fee of $99 million (the “Company Termination Fee”). The Company Termination Fee is payable under certain specified circumstances, including (i) termination of the Merger Agreement by the Company in order to enter into a definitive agreement with respect to certain business combinations, and (ii) termination of the Merger Agreement by Parent following a withdrawal by the Company Board of its recommendation of the Merger Agreement. The Company will also be required to pay Parent the Company Termination Fee in the event the Company signs an alternative transaction within twelve months following the termination of the Merger Agreement under certain specified circumstances. In addition, upon termination of the Merger Agreement in certain specified circumstances, the Company would be required to reimburse Parent for certain expenses incurred by Parent and its affiliates and representatives in connection with transaction, in an amount not to exceed $5 million . The Parent Termination Fee is payable by the Parent in certain specified circumstances if the Merger Agreement is terminated under certain circumstances due to the failure to obtain certain regulatory approvals as a result of the imposition of a Burdensome Condition or the material breach by Parent of its obligations to obtain certain regulatory approvals.

Basis of Presentation of Interi

Basis of Presentation of Interim Financial Statements	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation of Interim Financial Statements	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, 2015 . The preparation of financial statements and notes in conformity with GAAP requires that management make estimates and assumptions that affect the amounts of revenues, expenses, assets and liabilities, and disclosure of contingent assets and liabilities. Actual results could differ from estimates. The results of operations for the three and 12 months ended March 31, 2016 , are not necessarily indicative of the results that may be expected for the year ending December 31, 2016 . Certain reclassifications were made to prior year information to conform to the current year presentation. Questar and Questar Pipeline use the equity method to account for an investment in an unconsolidated affiliate where they do not have control, but have significant influence. The investment in the unconsolidated affiliate on the Condensed Consolidated Balance Sheets equals Questar Pipeline's proportionate share of equity reported by the unconsolidated affiliate. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below Questar Pipeline's carrying value. When such a condition is deemed to be other-than-temporary, the carrying value of the investment is written down to its fair value, and the amount of the write-down is included in the determination of net income. White River Hub, LLC, a limited liability company and FERC-regulated transporter of natural gas, is the sole unconsolidated affiliate. Questar Pipeline owns 50% of White River Hub, LLC, and is the operator. Questar Gas obtains the majority of its gas supply from Wexpro's cost-of-service production and pays Wexpro an operator service fee based on the terms of the Wexpro Agreement and the Wexpro II Agreement (Wexpro agreements). Questar Gas also obtains transportation and storage services from Questar Pipeline. These intercompany revenues and expenses are eliminated in the Questar Consolidated Statements of Income by reducing revenues and cost of sales. The underlying costs of Wexpro's production and Questar Pipeline's transportation and storage services are disclosed in other categories in the Consolidated Statements of Income, including operating and maintenance expense and depreciation, depletion and amortization expense. During the second and third quarters of the year, a significant portion of the natural gas from Wexpro production is injected into underground storage. This gas is withdrawn from storage as needed during the heating season in the first and fourth quarters. The cost of natural gas sold is credited with the value of natural gas as it is injected into storage and debited as it is withdrawn from storage. The reported balance in consolidated cost of sales may be a negative amount during the second and third quarters because of the entries to record injection of gas into storage and the elimination of intercompany transactions. The details of Questar's consolidated cost of sales are as follows: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Questar Gas Gas purchases $ 46.8 $ 41.0 $ 88.3 $ 84.8 Operator service fee 79.8 84.8 314.0 345.4 Transportation and storage 22.3 22.2 79.3 79.7 Gathering 5.8 5.4 22.5 21.5 Royalties 5.7 11.9 27.1 54.7 Storage (injection) withdrawal, net 36.7 30.9 2.3 (3.2 ) Purchased-gas account adjustment 58.6 36.2 42.9 (4.0 ) Other 1.2 1.2 5.0 4.9 Total Questar Gas cost of natural gas sold 256.9 233.6 581.4 583.8 Elimination of Questar Gas cost of natural gas sold - affiliated companies (99.0 ) (104.0 ) (388.5 ) (419.2 ) Total Questar Gas cost of natural gas sold - unaffiliated parties 157.9 129.6 192.9 164.6 Questar Pipeline Questar Pipeline cost of sales 0.1 1.9 7.1 4.2 Other cost of sales 0.5 0.3 1.9 1.1 Total cost of sales $ 158.5 $ 131.8 $ 201.9 $ 169.9

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic earnings per share (EPS) is computed by dividing net income by the weighted-average number of common shares outstanding during the reporting period, which includes vested undistributed restricted stock units (RSUs) and vested undistributed deferred RSUs. Diluted EPS includes the potential increase in the number of outstanding shares that could result from the exercise of in-the-money stock options, the vesting of RSUs with forfeitable dividend equivalents and the distribution of performance shares that are part of the Company's Long-Term Stock Incentive Plan (LTSIP), less shares repurchased under the treasury stock method. Restricted shares and RSUs with nonforfeitable dividends or dividend equivalents are participating securities for the computation of basic EPS under the two-class method. The application of the two-class method has an insignificant impact on the calculation of Questar's basic and diluted EPS. A reconciliation of the components of basic and diluted shares used in the EPS calculation follows: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Weighted-average basic common shares outstanding 175.8 176.2 175.9 176.0 Potential number of shares issuable under the Company's LTSIP 0.3 0.3 0.2 0.3 Weighted-average diluted common shares outstanding 176.1 176.5 176.1 176.3

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	3 Months Ended
	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income Comprehensive income, as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Consolidated Statements of Income and net other comprehensive income (loss) (OCI). OCI includes recognition of the under-funded position of pension and other postretirement benefit plans, interest rate and commodity-based cash flow hedges, changes in the fair value of long-term investment, and the related income taxes. Income or loss is recognized when the pension and other postretirement benefit (OPB) costs are accrued, as the Company records interest expense for hedged interest payments, as the Company reaches settlement of commodity-based hedges and when the long-term investment is sold. Details of the changes in the components of consolidated accumulated other comprehensive income (loss) (AOCI), net of income taxes, as reported in Questar's Condensed Consolidated Balance Sheets, are shown in the tables below. The tables also disclose details of income taxes related to each component of OCI. Pension and OPB Interest rate cash flow hedges Commodity cash flow hedges Long-term investment Total 3 Months Ended March 31, 2016 (in millions) AOCI at beginning of period $ (163.1 ) $ (22.2 ) $ (0.1 ) $ 0.1 $ (185.3 ) OCI before reclassifications — — (0.2 ) — (0.2 ) Reclassified from AOCI (1)(3) 4.0 0.2 — — 4.2 Income taxes Reclassified from AOCI (2)(4) (1.5 ) (0.1 ) — — (1.6 ) Total income taxes (1.5 ) (0.1 ) — — (1.6 ) Net other comprehensive income (loss) 2.5 0.1 (0.2 ) — 2.4 AOCI at end of period $ (160.6 ) $ (22.1 ) $ (0.3 ) $ 0.1 $ (182.9 ) Pension and OPB Interest rate cash flow hedges Long-term investment Total 3 Months Ended March 31, 2015 (in millions) AOCI at beginning of period $ (178.9 ) $ (22.5 ) $ 0.1 $ (201.3 ) Reclassified from AOCI (1) 6.0 0.2 — 6.2 Income taxes Reclassified from AOCI (2) (2.3 ) (0.1 ) — (2.4 ) Total income taxes (2.3 ) (0.1 ) — (2.4 ) Net other comprehensive income 3.7 0.1 — 3.8 AOCI at end of period $ (175.2 ) $ (22.4 ) $ 0.1 $ (197.5 ) (1) Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income. (2) Income tax reclassifications related to interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income. (3) Commodity cash flow hedge amounts are included in their entirety as an increase in Questar Pipeline revenue on the Consolidated Statements of Income. (4) Income tax reclassifications related to commodity cash flow hedge amounts are included in their entirety as charges to income taxes on the Consolidated Statements of Income. Pension and other postretirement benefit AOCI reclassifications are included in the computation of net periodic pension and postretirement benefit costs. See Note 10 for additional details. Disclosures regarding interest rate and commodity-based cash flow hedges, including income taxes and income statement reclassification effects, apply to Questar Pipeline.

Asset Retirement Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 2016
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations Questar records an asset retirement obligation (ARO) along with an increase to the carrying value of the related property, plant and equipment when there is a legal obligation associated with the retirement of a tangible long-lived asset. Questar's AROs apply primarily to abandonment costs associated with gas and oil wells, production facilities and certain other properties. The Company has not recorded AROs on a majority of its long-lived transportation and distribution assets because the Company does not have a legal obligation to restore the area surrounding abandoned assets. The fair value of retirement costs is estimated by Company personnel based on abandonment costs of similar properties available to field operations and depreciated over the life of the related assets. Revisions to estimates result from material changes in the expected timing or amount of cash flows associated with AROs. Income or expense resulting from the settlement of ARO liabilities is included in net gain (loss) from asset sales on the Consolidated Statements of Income. The ARO liability is adjusted to present value each period through an accretion calculation using a credit-adjusted risk-free interest rate. Changes in Questar's AROs from the Condensed Consolidated Balance Sheets were as follows: 3 Months Ended March 31, 2016 2015 (in millions) AROs at beginning of year $ 67.6 $ 69.3 Accretion 1.0 0.8 Liabilities incurred 0.2 0.1 Revisions in estimated cash flows 2.1 5.7 Liabilities settled (0.4 ) (0.9 ) AROs at end of period $ 70.5 $ 75.0 Wexpro collects from Questar Gas and deposits in trust certain funds related to AROs. The funds are recorded as other noncurrent assets and used to satisfy retirement obligations as the properties are abandoned. The accounting treatment of reclamation activities associated with AROs for properties administered under the Wexpro agreements is defined in a guideline letter between Wexpro and the Utah Division of Public Utilities and the staff of the Wyoming Public Service Commission.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Questar complies with the accounting standards for fair value measurements and disclosures. The standards establish a fair value hierarchy. Level 1 inputs are unadjusted quoted prices for identical assets or liabilities in active markets that the Company has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 inputs are unobservable inputs for the asset or liability. The Company had no assets or liabilities measured using Level 3 inputs at March 31, 2016 , March 31, 2015 , or December 31, 2015 . Fair value accounting standards also apply to certain nonfinancial assets and liabilities that are measured at fair value on a nonrecurring basis. At December 31, 2015 , the Company recorded a pre-tax abandonment and impairment charge of $12.1 million for the South Moxa leasehold. Thus, the South Moxa leasehold was reported at fair value on a nonrecurring basis at December 31, 2015 . Questar did not have any assets or liabilities measured at fair value on a nonrecurring basis at March 31, 2016 or March 31, 2015 . Questar The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar's financial statements in this Quarterly Report: Hierarchy Level of Fair Value Estimates Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value March 31, 2016 March 31, 2015 Dec. 31, 2015 (in millions) Financial assets Cash and cash equivalents 1 $ 0.4 $ 0.4 $ 4.8 $ 4.8 $ 25.0 $ 25.0 Long-term investment 1 15.1 15.1 16.2 16.2 14.1 14.1 Financial liabilities Short-term debt 1 458.5 458.5 214.0 214.0 457.6 457.6 Long-term debt, including current portion 2 957.0 1,050.4 1,231.8 1,396.3 1,206.7 1,263.7 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 6). The fair value of the long-term investment is based on quoted prices for the underlying funds. The fair value of fixed-rate long-term debt is based on the discounted present value of cash flows using the Company's current credit risk-adjusted borrowing rates. Questar Gas The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Gas's financial statements in this Quarterly Report: Hierarchy Level of Fair Value Estimates Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value March 31, 2016 March 31, 2015 Dec. 31, 2015 (in millions) Financial assets Cash and cash equivalents 1 $ — $ — $ — $ — $ 10.5 $ 10.5 Financial liabilities Checks outstanding in excess of cash balances 1 0.7 0.7 0.4 0.4 — — Notes payable to Questar 1 140.5 140.5 35.8 35.8 273.3 273.3 Long-term debt 2 527.6 591.7 526.8 629.0 527.4 568.4 The carrying amounts of notes payable to Questar approximate fair value because of their short maturities and market-based interest rates. The fair value of fixed-rate long-term debt is based on the discounted present value of cash flows using Questar Gas's current credit risk-adjusted borrowing rates. Questar Pipeline The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Pipeline's financial statements in this Quarterly Report: Hierarchy Level of Fair Value Estimates Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value March 31, 2016 March 31, 2015 Dec. 31, 2015 (in millions) Financial assets Cash and cash equivalents 1 $ 1.2 $ 1.2 $ 6.1 $ 6.1 $ 10.2 $ 10.2 Notes receivable from Questar 1 33.2 33.2 35.9 35.9 6.0 6.0 Financial liabilities Long-term debt, including current portion 2 429.4 458.7 453.9 515.1 429.2 445.2 The carrying amounts of notes receivable from Questar approximate fair value because of their short maturities and market-based interest rates. The fair value of fixed-rate long-term debt is based on the discounted present value of cash flows using Questar Pipeline's current credit risk-adjusted borrowing rates.

Derivatives and Hedging

Derivatives and Hedging	3 Months Ended
	Mar. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging	Derivatives and Hedging Questar and its subsidiaries may enter into derivative instruments to manage exposure to changes in current and future market interest rates. Questar Pipeline entered into forward starting swaps totaling $150.0 million in the second and third quarters of 2011 in anticipation of issuing $180.0 million of notes in December 2011. Settlement of these swaps required payments of $37.3 million in the fourth quarter of 2011 because of declines in interest rates. These swaps qualified as cash flow hedges and the settlement payments are being amortized to interest expense over the 30 -year life of the debt. See the Condensed Consolidated Statements of Comprehensive Income and Note 5 for details regarding reclassifications of AOCI related to deferred interest rate cash flow hedge losses to interest expense for the three months ended March 31, 2016 and March 31, 2015 . 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 . There was a $0.4 million liability at March 31, 2016 , and a $0.2 million liability at December 31, 2015 . There were no derivative assets or liabilities outstanding at March 31, 2015 .

Operations by Line of Business

Operations by Line of Business	3 Months Ended
	Mar. 31, 2016
Segment Reporting [Abstract]
Operations by Line of Business	Operations by Line of Business Questar's three principal complementary lines of business include Questar Gas, which provides retail natural gas distribution in Utah, Wyoming and Idaho; Wexpro, which develops and produces natural gas from cost-of-service reserves for Questar Gas customers; and Questar Pipeline, which operates interstate natural gas pipelines and storage facilities and provides other energy services. Line-of-business information is presented according to senior management's basis for evaluating performance and considering differences in the nature of products, services and regulation, among other factors. Following is a summary of operations by line of business: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Revenues from Unaffiliated Customers Questar Gas $ 407.9 $ 374.8 $ 950.7 $ 939.4 Wexpro 3.5 6.3 20.1 29.6 Questar Pipeline 43.0 46.8 184.1 189.0 Other 1.9 0.7 7.7 3.0 Total $ 456.3 $ 428.6 $ 1,162.6 $ 1,161.0 Revenues from Affiliated Companies Wexpro $ 79.8 $ 84.8 $ 314.1 $ 346.0 Questar Pipeline 19.3 19.4 75.0 73.8 Total $ 99.1 $ 104.2 $ 389.1 $ 419.8 Operating Income (Loss) Questar Gas $ 83.4 $ 76.6 $ 129.4 $ 116.3 Wexpro 39.7 41.7 145.4 176.5 Questar Pipeline 27.6 27.4 114.6 114.9 Corporate and other (15.0 ) 1.3 (26.3 ) (3.6 ) Total $ 135.7 $ 147.0 $ 363.1 $ 404.1 Net Income (Loss) Questar Gas $ 47.6 $ 43.8 $ 68.1 $ 59.4 Wexpro 26.2 27.7 97.4 118.7 Questar Pipeline 14.2 13.9 59.9 58.8 Corporate and other (9.5 ) (0.8 ) (22.8 ) (10.9 ) Total $ 78.5 $ 84.6 $ 202.6 $ 226.0

Employee Benefits

Employee Benefits	3 Months Ended
	Mar. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Employee Benefits	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 2016 estimated net cost for the qualified pension plan is $8.2 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, above the benefit limit defined by the Internal Revenue Service (IRS) for the qualified plan. The nonqualified pension plan is unfunded; benefits are paid from the Company's general funds. The 2016 estimated net cost for the nonqualified pension plan is $3.0 million . Components of the qualified and nonqualified net periodic pension cost are listed in the table below: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Service cost $ 3.0 $ 3.4 $ 13.4 $ 12.2 Interest cost 8.2 8.1 32.8 33.1 Expected return on plan assets (12.2 ) (11.6 ) (48.3 ) (44.6 ) Prior service cost — — 0.1 0.5 Recognized net actuarial loss 3.8 5.7 20.0 17.2 Pension settlement costs — — 16.7 — Net pension cost $ 2.8 $ 5.6 $ 34.7 $ 18.4 The Company currently estimates a $2.1 million net cost for postretirement benefits other than pensions in 2016 , before accretion of a regulatory liability. Net periodic postretirement benefit cost components are listed in the table below: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Service cost $ 0.1 $ 0.2 $ 0.5 $ 0.6 Interest cost 0.9 0.9 3.5 3.7 Expected return on plan assets (0.7 ) (0.8 ) (3.1 ) (3.0 ) Recognized net actuarial loss 0.2 0.3 1.1 0.7 Accretion of regulatory liability 0.2 0.2 1.0 0.8 Net postretirement benefit cost $ 0.7 $ 0.8 $ 3.0 $ 2.8

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies Questar and each of its subsidiaries are involved in various commercial, environmental, and regulatory claims. Litigation and other legal proceedings arise in the ordinary course of business. Management does not believe any such litigation or other legal proceedings arising in the ordinary course of business individually or in the aggregate, will have a material adverse effect on Questar's, Questar Gas's or Questar Pipeline's financial position, results of operations or cash flows. A liability is recorded for a loss contingency when its occurrence is probable and its amount can be reasonably estimated. If some amount within a range of possible outcomes appears to be a better estimate than any other amount within the range, that amount is recorded. Otherwise, the minimum amount in the range is recorded. Disclosures are provided for contingencies reasonably likely to occur, which would have a material adverse effect on Questar's, Questar Gas's or Questar Pipeline's financial position, results of operations or cash flows. Some of the claims involve highly complex issues relating to liability, damages and other matters subject to substantial uncertainties and, therefore, the probability of liability or an estimate of loss cannot be reasonably determined. Litigation The case related to operations entitled Questar Gas Company v. QEP Field Services Company that was filed in Third District Court in Salt Lake County, Utah on May 1, 2012, was settled on March 22, 2016. Questar Gas believes the settlement agreement reasonably resolves disputed issues regarding services and charges under the 1993 Gas Gathering Agreement. The settlement agreement did not result in a material impact on Questar's or Questar Gas's results of operation, financial position or cash flows. In February 2015, a trial was held in the case of Rocky Mountain Resources and Robert N. Floyd v. QEP Energy Company and Wexpro Company , Ninth Judicial District, County of Sublette, State of Wyoming, Case No. 2011-7816. Plaintiffs allege they are entitled to a 4% overriding royalty interest (ORRI) in a so-called replacement state oil and gas lease ultimately assigned to Wexpro and QEP Energy Company (QEP) in the Pinedale Field. Wexpro and QEP believe the former state leases subject to the ORRI expired and a new lease was issued by the State of Wyoming unburdened by the 4% ORRI. A jury decision was reached on February 13, 2015, that awarded the Plaintiffs $14.1 million from Wexpro and $16.2 million from QEP. Wexpro and QEP have filed an appeal of the case to the Wyoming Supreme Court and briefing begins in May 2016. Wexpro has accrued its estimate of liability in the case. Any additional royalties will be recovered from Questar Gas’s customers. Litigation Related to Proposed Merger As more fully described in Note 2, Questar entered into an Agreement and Plan of Merger with Dominion Resources, Inc. ("Dominion Resources") and its wholly-owned subsidiary, Diamond Beehive Corp. on January 31, 2016 , pursuant to which Questar shareholders have the right to receive $25.00 per share in cash, subject to the satisfaction of specified conditions. If the Dominion Merger is completed, Questar will become a wholly-owned subsidiary of Dominion Resources. As of April 25, 2016, six lawsuits challenging the Merger have been filed purportedly on behalf of Questar shareholders, of which four are pending in the Third District Court, Salt Lake County, Utah, and two are pending in the United States District Court of Utah, Central Division. Each of the lawsuits names Questar, Questar’s directors, Dominion Resources and Diamond Beehive Corp. as defendants. The named plaintiffs in the four lawsuits pending in Third District Court are John Hansen, Eric Senatori, Shiva Stein and James E. Toth, and Teamsters Local 456 Pension Fund and Teamsters Local 456 Annuity Fund, respectively. The named plaintiffs in the two lawsuits pending in U.S. District Court are Kevin Hessel and Dan Ipson, respectively. All of the lawsuits are purported shareholder class actions advancing substantially the same allegations that the Merger Agreement was adopted in violation of the fiduciary duties of Questar’s directors and seeking injunctive relief to enjoin the Dominion Merger, as well as other remedies. All of the cases raise direct claims on behalf of Questar shareholders. In addition, one of the cases raises derivative claims on behalf of Questar. On April 21, 2016, the Third District Court granted a request to consolidate all four cases pending in Third District Court into Teamsters Local 456 Pension Fund, et. al. v. Ronald W. Jibson, et. al. (Case No. 160900938). On April 22, 2016, the court appointed Teamsters Local 456 Pension Fund as lead plaintiff in the consolidated matter. The court also appointed lead counsel and liaison counsel. The court scheduled a preliminary injunction hearing for May 9, 2016. The cases pending in U.S. District Court are voluntarily stayed pending the outcome of the preliminary injunction hearing in Third District Court. The outcome of these lawsuits is uncertain, and additional lawsuits may be brought or additional claims advanced concerning the Merger. An adverse judgment for monetary damages could have an adverse effect on Questar’s operations. A preliminary injunction could delay or jeopardize the completion of the Merger, and an adverse judgment granting permanent injunctive relief could indefinitely enjoin completion of the Merger.

Asset Impairments

Asset Impairments	3 Months Ended
	Mar. 31, 2016
Wexpro Impairment [Abstract]
Asset Impairments	Asset Impairments During the fourth quarter of 2015, Wexpro recorded a pre-tax abandonment and impairment charge of $12.1 million for the South Moxa leasehold because current market prices do not support a drilling program.

Accounting Developments

Accounting Developments	3 Months Ended
	Mar. 31, 2016
Recent Accounting Developments [Abstract]
Recent Accounting Developments	Accounting Developments In April 2016, The Financial Accounting Standards Board (FASB) issued Accounting Standards Updates (ASU) 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing . This update is due to issues regarding performance obligations and licensing identified by the Transition Resource Group for Revenue Recognition. The amendments in this update do not change the core principle of the guidance in Topic 606, Revenue from Contracts with Customers. Rather, the amendments in this Update clarify the following two aspects of Topic 606: identifying performance obligations and the licensing implementation guidance, while retaining the related principles for those areas. The effective date for the amendments in this update is the same as ASU 2015-14 noted below. The Company is currently evaluating the ASU's effect on its financial position, results of operations or cash flows. In March 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation: Improvements to Employee Share-Based Payment Accounting . The ASU was issued a part of the Board simplification initiative. The areas for simplification in this Update involve several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. In addition to those simplifications, the amendments eliminate the guidance in Topic 718 that was indefinitely deferred shortly after the issuance of FASB Statement No. 123 (revised 2004), Share-Based Payment. This should not result in a change in practice because the guidance that is being superseded was never effective. the amendments in this Update are effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. The Company is currently evaluating the ASU's effect on its financial position, results of operations or cash flows. In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations . This updated is the result of feedback received by the Transition Resource Group for Revenue Recognition. The amendments in this update are intended to improve the operability and understandability of the implementation guidance on principal versus agent considerations as outlined in Topic 606. The effective date for the amendments in this update is the same as ASU 2015-14 noted below. The Company is currently evaluating the ASU's effect on its financial position, results of operations or cash flows. In February 2016, the FASB issued ASU 2016-02, Leases . The ASU was issued to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. To meet that objective, the FASB is amending the FASB Accounting Standards Codification and creating Topic 842, Leases. The update mainly addresses issues with accounting for operating leases in the financial statements of lessees. As such, the amendments of this update do not fundamentally change lessor accounting. However, some changes have been made to lessor accounting to conform and align that guidance with the lessee guidance and other areas within generally accepted accounting principles. The amendments in this Update are effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company is currently evaluating the ASU's effect on its financial position, results of operations, cash flows and associated disclosures. In January 2016, FASB issued ASU 2016-01, Financial Instruments-Overall . The ASU was developed to enhance the reporting model for financial instruments in order to provide users of financial statements with more decision-useful information. The update addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company is currently evaluating the ASU's effect on its financial position, results of operations, cash flows and associated disclosures. In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes . The ASU simplifies the presentation of deferred income taxes. The update requires that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. The guidance will be effective for annual periods beginning after December 15, 2016. The Company has adopted this update for the current reporting period and has retrospectively reflected all deferred taxes as noncurrent for the periods presented. In August 2015, the FASB issued ASU 2015-15, Interest—Imputation of Interest (Subtopic 835-30): Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of-Credit Arrangements—Amendments to SEC Paragraphs Pursuant to Staff Announcement at June 18, 2015 EITF Meeting (SEC Update) . This update adds SEC staff guidance to the Codification that the SEC staff will not object to an entity presenting the costs of securing line-of-credit arrangements as an asset, regardless of whether there are any outstanding borrowings. The guidance was issued in response to questions that arose after the FASB issued ASU 2015-03, Interest - Imputation of Interest (Subtopic 835-30) - Simplifying the Presentation of Debt Issuance Costs, in April 2015. The Company has adopted ASU 2015-03 for the current reporting period and has retrospectively adjusted all periods presented. The prior period debt issuance costs (asset) were netted against the debt within the liability section of the balance sheet. The resulting effect on the balance sheet was a reduction in assets with a corresponding reduction in liabilities. In August 2015, the FASB issued ASU 2015-14. This update defers the effective date of ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which the FASB issued in May of 2014, by one year. ASU 2014-09 replaces most of the existing revenue guidance with a single set of principles, including changes in recognition and disclosure requirements. The revised effective date will be January 1, 2018 and early adoption is permitted beginning January 1, 2017. The new guidance must be applied retrospectively for each prior period presented or via a cumulative effect upon the date of initial application. The Company is currently evaluating the ASU's effect on its financial position, results of operations or cash flows, as well as which transition approach it will take. In July 2015, the FASB issued ASU 2015-11, Inventory (Topic 330) . The ASU states that inventory should be measured at the lower of cost and net realizable value. The guidance will be effective beginning January 1, 2017 and will be applied prospectively. The Company is currently evaluating the ASU's effect on its financial position, results of operations and cash flows. In April 2015, the FASB issued ASU 2015-03, Interest - Imputation of Interest (Subtopic 835-30) . The ASU simplifies the presentation of debt issuance costs by requiring that the debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. The guidance will be effective beginning January 1, 2016 and early adoption is permitted. The new guidance must be applied retrospectively for each prior period presented. The Company has adopted this update for the current reporting period and has retrospectively adjusted all periods presented.

Basis of Presentation of Inte19

Basis of Presentation of Interim Financial Statements (Policies)	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Questar Corporation (the Company) is a Rockies-based integrated natural gas company with three principal complementary and wholly-owned lines of business: • Questar Gas Company (Questar Gas) provides retail natural gas distribution in Utah, Wyoming and Idaho. • Wexpro Company (Wexpro) develops and produces natural gas from cost-of-service reserves for Questar Gas customers. • Questar Pipeline Company (Questar Pipeline) operates interstate natural gas pipelines and storage facilities in the western United States and provides other energy services. Questar is headquartered in Salt Lake City, Utah. Shares of Questar common stock trade on the New York Stock Exchange (NYSE:STR).
Investment in Unconsolidated Affiliate	Questar and Questar Pipeline use the equity method to account for an investment in an unconsolidated affiliate where they do not have control, but have significant influence. The investment in the unconsolidated affiliate on the Condensed Consolidated Balance Sheets equals Questar Pipeline's proportionate share of equity reported by the unconsolidated affiliate. The investment is assessed for possible impairment when events indicate that the fair value of the investment may be below Questar Pipeline's carrying value. When such a condition is deemed to be other-than-temporary, the carrying value of the investment is written down to its fair value, and the amount of the write-down is included in the determination of net income. White River Hub, LLC, a limited liability company and FERC-regulated transporter of natural gas, is the sole unconsolidated affiliate. Questar Pipeline owns 50% of White River Hub, LLC, and is the operator.
Earnings Per Share	Basic earnings per share (EPS) is computed by dividing net income by the weighted-average number of common shares outstanding during the reporting period, which includes vested undistributed restricted stock units (RSUs) and vested undistributed deferred RSUs. Diluted EPS includes the potential increase in the number of outstanding shares that could result from the exercise of in-the-money stock options, the vesting of RSUs with forfeitable dividend equivalents and the distribution of performance shares that are part of the Company's Long-Term Stock Incentive Plan (LTSIP), less shares repurchased under the treasury stock method. Restricted shares and RSUs with nonforfeitable dividends or dividend equivalents are participating securities for the computation of basic EPS under the two-class method. The application of the two-class method has an insignificant impact on the calculation of Questar's basic and diluted EPS.
Comprehensive Income - Questar	Comprehensive income, as reported in Questar's Condensed Consolidated Statements of Comprehensive Income, is the sum of net income as reported in the Questar Consolidated Statements of Income and net other comprehensive income (loss) (OCI). OCI includes recognition of the under-funded position of pension and other postretirement benefit plans, interest rate and commodity-based cash flow hedges, changes in the fair value of long-term investment, and the related income taxes. Income or loss is recognized when the pension and other postretirement benefit (OPB) costs are accrued, as the Company records interest expense for hedged interest payments, as the Company reaches settlement of commodity-based hedges and when the long-term investment is sold.
Comprehensive Income - Questar Pipeline	Disclosures regarding interest rate and commodity-based cash flow hedges, including income taxes and income statement reclassification effects, apply to Questar Pipeline.
Asset Retirement Obligations	Questar records an asset retirement obligation (ARO) along with an increase to the carrying value of the related property, plant and equipment when there is a legal obligation associated with the retirement of a tangible long-lived asset. Questar's AROs apply primarily to abandonment costs associated with gas and oil wells, production facilities and certain other properties. The Company has not recorded AROs on a majority of its long-lived transportation and distribution assets because the Company does not have a legal obligation to restore the area surrounding abandoned assets. The fair value of retirement costs is estimated by Company personnel based on abandonment costs of similar properties available to field operations and depreciated over the life of the related assets. Revisions to estimates result from material changes in the expected timing or amount of cash flows associated with AROs. Income or expense resulting from the settlement of ARO liabilities is included in net gain (loss) from asset sales on the Consolidated Statements of Income. The ARO liability is adjusted to present value each period through an accretion calculation using a credit-adjusted risk-free interest rate.
Business Segments	Line-of-business information is presented according to senior management's basis for evaluating performance and considering differences in the nature of products, services and regulation, among other factors.
Contingencies	A liability is recorded for a loss contingency when its occurrence is probable and its amount can be reasonably estimated. If some amount within a range of possible outcomes appears to be a better estimate than any other amount within the range, that amount is recorded. Otherwise, the minimum amount in the range is recorded. Disclosures are provided for contingencies reasonably likely to occur, which would have a material adverse effect on Questar's, Questar Gas's or Questar Pipeline's financial position, results of operations or cash flows. Some of the claims involve highly complex issues relating to liability, damages and other matters subject to substantial uncertainties and, therefore, the probability of liability or an estimate of loss cannot be reasonably determined.

Basis of Presentation of Inte20

Basis of Presentation of Interim Financial Statements (Tables)	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cost of sales detail	The details of Questar's consolidated cost of sales are as follows: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Questar Gas Gas purchases $ 46.8 $ 41.0 $ 88.3 $ 84.8 Operator service fee 79.8 84.8 314.0 345.4 Transportation and storage 22.3 22.2 79.3 79.7 Gathering 5.8 5.4 22.5 21.5 Royalties 5.7 11.9 27.1 54.7 Storage (injection) withdrawal, net 36.7 30.9 2.3 (3.2 ) Purchased-gas account adjustment 58.6 36.2 42.9 (4.0 ) Other 1.2 1.2 5.0 4.9 Total Questar Gas cost of natural gas sold 256.9 233.6 581.4 583.8 Elimination of Questar Gas cost of natural gas sold - affiliated companies (99.0 ) (104.0 ) (388.5 ) (419.2 ) Total Questar Gas cost of natural gas sold - unaffiliated parties 157.9 129.6 192.9 164.6 Questar Pipeline Questar Pipeline cost of sales 0.1 1.9 7.1 4.2 Other cost of sales 0.5 0.3 1.9 1.1 Total cost of sales $ 158.5 $ 131.8 $ 201.9 $ 169.9

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Schedule of Weighted Average Number of Shares	A reconciliation of the components of basic and diluted shares used in the EPS calculation follows: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Weighted-average basic common shares outstanding 175.8 176.2 175.9 176.0 Potential number of shares issuable under the Company's LTSIP 0.3 0.3 0.2 0.3 Weighted-average diluted common shares outstanding 176.1 176.5 176.1 176.3

Accumulated Other Comprehensi22

Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	Details of the changes in the components of consolidated accumulated other comprehensive income (loss) (AOCI), net of income taxes, as reported in Questar's Condensed Consolidated Balance Sheets, are shown in the tables below. The tables also disclose details of income taxes related to each component of OCI. Pension and OPB Interest rate cash flow hedges Commodity cash flow hedges Long-term investment Total 3 Months Ended March 31, 2016 (in millions) AOCI at beginning of period $ (163.1 ) $ (22.2 ) $ (0.1 ) $ 0.1 $ (185.3 ) OCI before reclassifications — — (0.2 ) — (0.2 ) Reclassified from AOCI (1)(3) 4.0 0.2 — — 4.2 Income taxes Reclassified from AOCI (2)(4) (1.5 ) (0.1 ) — — (1.6 ) Total income taxes (1.5 ) (0.1 ) — — (1.6 ) Net other comprehensive income (loss) 2.5 0.1 (0.2 ) — 2.4 AOCI at end of period $ (160.6 ) $ (22.1 ) $ (0.3 ) $ 0.1 $ (182.9 ) Pension and OPB Interest rate cash flow hedges Long-term investment Total 3 Months Ended March 31, 2015 (in millions) AOCI at beginning of period $ (178.9 ) $ (22.5 ) $ 0.1 $ (201.3 ) Reclassified from AOCI (1) 6.0 0.2 — 6.2 Income taxes Reclassified from AOCI (2) (2.3 ) (0.1 ) — (2.4 ) Total income taxes (2.3 ) (0.1 ) — (2.4 ) Net other comprehensive income 3.7 0.1 — 3.8 AOCI at end of period $ (175.2 ) $ (22.4 ) $ 0.1 $ (197.5 ) (1) Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income. (2) Income tax reclassifications related to interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income. (3) Commodity cash flow hedge amounts are included in their entirety as an increase in Questar Pipeline revenue on the Consolidated Statements of Income. (4) Income tax reclassifications related to commodity cash flow hedge amounts are included in their entirety as charges to income taxes on the Consolidated Statements of Income.

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 2016
Asset Retirement Obligation [Abstract]
Changes in AROs	Changes in Questar's AROs from the Condensed Consolidated Balance Sheets were as follows: 3 Months Ended March 31, 2016 2015 (in millions) AROs at beginning of year $ 67.6 $ 69.3 Accretion 1.0 0.8 Liabilities incurred 0.2 0.1 Revisions in estimated cash flows 2.1 5.7 Liabilities settled (0.4 ) (0.9 ) AROs at end of period $ 70.5 $ 75.0

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, by Balance Sheet Grouping	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar's financial statements in this Quarterly Report: Hierarchy Level of Fair Value Estimates Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value March 31, 2016 March 31, 2015 Dec. 31, 2015 (in millions) Financial assets Cash and cash equivalents 1 $ 0.4 $ 0.4 $ 4.8 $ 4.8 $ 25.0 $ 25.0 Long-term investment 1 15.1 15.1 16.2 16.2 14.1 14.1 Financial liabilities Short-term debt 1 458.5 458.5 214.0 214.0 457.6 457.6 Long-term debt, including current portion 2 957.0 1,050.4 1,231.8 1,396.3 1,206.7 1,263.7
Questar Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, by Balance Sheet Grouping	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Gas's financial statements in this Quarterly Report: Hierarchy Level of Fair Value Estimates Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value March 31, 2016 March 31, 2015 Dec. 31, 2015 (in millions) Financial assets Cash and cash equivalents 1 $ — $ — $ — $ — $ 10.5 $ 10.5 Financial liabilities Checks outstanding in excess of cash balances 1 0.7 0.7 0.4 0.4 — — Notes payable to Questar 1 140.5 140.5 35.8 35.8 273.3 273.3 Long-term debt 2 527.6 591.7 526.8 629.0 527.4 568.4
Questar Pipeline [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, by Balance Sheet Grouping	The following table discloses the carrying amount, estimated fair value and level within the fair value hierarchy of certain financial instruments not disclosed in other notes to Questar Pipeline's financial statements in this Quarterly Report: Hierarchy Level of Fair Value Estimates Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value March 31, 2016 March 31, 2015 Dec. 31, 2015 (in millions) Financial assets Cash and cash equivalents 1 $ 1.2 $ 1.2 $ 6.1 $ 6.1 $ 10.2 $ 10.2 Notes receivable from Questar 1 33.2 33.2 35.9 35.9 6.0 6.0 Financial liabilities Long-term debt, including current portion 2 429.4 458.7 453.9 515.1 429.2 445.2

Operations by Line of Business

Operations by Line of Business (Tables)	3 Months Ended
	Mar. 31, 2016
Segment Reporting [Abstract]
Summary of operations by line of business	Following is a summary of operations by line of business: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Revenues from Unaffiliated Customers Questar Gas $ 407.9 $ 374.8 $ 950.7 $ 939.4 Wexpro 3.5 6.3 20.1 29.6 Questar Pipeline 43.0 46.8 184.1 189.0 Other 1.9 0.7 7.7 3.0 Total $ 456.3 $ 428.6 $ 1,162.6 $ 1,161.0 Revenues from Affiliated Companies Wexpro $ 79.8 $ 84.8 $ 314.1 $ 346.0 Questar Pipeline 19.3 19.4 75.0 73.8 Total $ 99.1 $ 104.2 $ 389.1 $ 419.8 Operating Income (Loss) Questar Gas $ 83.4 $ 76.6 $ 129.4 $ 116.3 Wexpro 39.7 41.7 145.4 176.5 Questar Pipeline 27.6 27.4 114.6 114.9 Corporate and other (15.0 ) 1.3 (26.3 ) (3.6 ) Total $ 135.7 $ 147.0 $ 363.1 $ 404.1 Net Income (Loss) Questar Gas $ 47.6 $ 43.8 $ 68.1 $ 59.4 Wexpro 26.2 27.7 97.4 118.7 Questar Pipeline 14.2 13.9 59.9 58.8 Corporate and other (9.5 ) (0.8 ) (22.8 ) (10.9 ) Total $ 78.5 $ 84.6 $ 202.6 $ 226.0

Employee Benefits (Tables)

Employee Benefits (Tables)	3 Months Ended
	Mar. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Schedule of Defined Benefit Plans Disclosures	Net periodic postretirement benefit cost components are listed in the table below: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Service cost $ 0.1 $ 0.2 $ 0.5 $ 0.6 Interest cost 0.9 0.9 3.5 3.7 Expected return on plan assets (0.7 ) (0.8 ) (3.1 ) (3.0 ) Recognized net actuarial loss 0.2 0.3 1.1 0.7 Accretion of regulatory liability 0.2 0.2 1.0 0.8 Net postretirement benefit cost $ 0.7 $ 0.8 $ 3.0 $ 2.8 Components of the qualified and nonqualified net periodic pension cost are listed in the table below: 3 Months Ended 12 Months Ended March 31, March 31, 2016 2015 2016 2015 (in millions) Service cost $ 3.0 $ 3.4 $ 13.4 $ 12.2 Interest cost 8.2 8.1 32.8 33.1 Expected return on plan assets (12.2 ) (11.6 ) (48.3 ) (44.6 ) Prior service cost — — 0.1 0.5 Recognized net actuarial loss 3.8 5.7 20.0 17.2 Pension settlement costs — — 16.7 — Net pension cost $ 2.8 $ 5.6 $ 34.7 $ 18.4

Nature of Business (Details)

Nature of Business (Details)	3 Months Ended
	Mar. 31, 2016lines_of_business
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of principal complementary lines of business	3

Proposed Merger with Dominion28

Proposed Merger with Dominion Resources (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)$ / shares
Business Combinations [Abstract]
Business Acquisition, Date of Acquisition Agreement	Jan. 31, 2016
Business Acquisition, Share Price | $ / shares	$ 25
Maximum Extension to Merger Agreement	9 months
Business Acquisition, Acquirer Termination Fee	$ 154
Business Acquisition, Acquiree Termination Fee	$ 99
Alternative Transaction Period	12 months
Business Acquisition Acquiree Reimbursement Fee	$ 5

Basis of Presentation of Inte29

Basis of Presentation of Interim Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Cost of Sales [Abstract]
Other cost of sales	$ 0.5	$ 0.3	$ 1.9	$ 1.1
Total cost of sales	158.5	131.8	201.9	169.9
Questar Gas [Member]
Cost of Sales [Abstract]
Gas purchases	46.8	41	88.3	84.8
Operator service fee	79.8	84.8	314	345.4
Transportation and storage	22.3	22.2	79.3	79.7
Gathering	5.8	5.4	22.5	21.5
Royalties	5.7	11.9	27.1	54.7
Storage (injection) withdrawal, net	36.7	30.9	2.3	(3.2)
Purchased-gas account adjustment	58.6	36.2	42.9	(4)
Other	1.2	1.2	5	4.9
Total Questar Gas cost of natural gas sold	256.9	233.6	581.4	583.8
Elimination of Questar Gas cost of natural gas sold - affiliated companies	(99)	(104)	(388.5)	(419.2)
Total Questar Gas cost of natural gas sold - unaffiliated parties	$ 157.9	129.6	$ 192.9	164.6
Questar Pipeline [Member]
Ownership percentage in unconsolidated affiliate (in hundredths)	50.00%		50.00%
Cost of Sales [Abstract]
Questar Pipeline cost of sales	$ 0.1	$ 1.9	$ 7.1	$ 4.2

Earnings Per Share (Details)

Earnings Per Share (Details) - shares shares in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Weighted-average basic common shares outstanding (in shares)	175.8	176.2	175.9	176
Potential number of shares issuable under the Company's LTSIP (in shares)	0.3	0.3	0.2	0.3
Weighted-average diluted common shares outstanding (in shares)	176.1	176.5	176.1	176.3

Accumulated Other Comprehensi31

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
		Mar. 31, 2016		Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period		$ (185.3)		$ (201.3)	$ (197.5)
OCI before reclassifications		(0.2)
Reclassified from AOCI	[2]	4.2	[1]	6.2
Income taxes
Reclassified from AOCI	[4]	(1.6)	[3]	(2.4)
Total income taxes		(1.6)		(2.4)	(9.2)	$ 36.3
Net other comprehensive income (loss)		2.4		3.8	14.6	(58.4)
AOCI at end of period		(182.9)		(197.5)	(182.9)	(197.5)
Pension and OPB
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period		(163.1)		(178.9)	(175.2)
OCI before reclassifications		0
Reclassified from AOCI	[2]	4	[1]	6
Income taxes
Reclassified from AOCI	[4]	(1.5)	[3]	(2.3)
Total income taxes		(1.5)		(2.3)
Net other comprehensive income (loss)		2.5		3.7
AOCI at end of period		(160.6)		(175.2)	(160.6)	(175.2)
Interest rate cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period		(22.2)		(22.5)	(22.4)
OCI before reclassifications		0
Reclassified from AOCI	[2]	0.2	[1]	0.2
Income taxes
Reclassified from AOCI	[4]	(0.1)	[3]	(0.1)
Total income taxes		(0.1)		(0.1)
Net other comprehensive income (loss)		0.1		0.1
AOCI at end of period		(22.1)		(22.4)	(22.1)	(22.4)
Commodity cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period		(0.1)
OCI before reclassifications		(0.2)
Reclassified from AOCI	[1],[2]	0
Income taxes
Reclassified from AOCI	[3],[4]	0
Total income taxes		0
Net other comprehensive income (loss)		(0.2)
AOCI at end of period		(0.3)			(0.3)
Long-term investment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
AOCI at beginning of period		0.1		0.1	0.1
OCI before reclassifications		0
Reclassified from AOCI	[2]	0	[1]	0
Income taxes
Reclassified from AOCI	[4]	0	[3]	0
Total income taxes		0		0
Net other comprehensive income (loss)		0		0
AOCI at end of period		$ 0.1		$ 0.1	$ 0.1	$ 0.1
[1]	Commodity cash flow hedge amounts are included in their entirety as an increase in Questar Pipeline revenue on the Consolidated Statements of Income.
[2]	Interest rate cash flow hedge amounts are included in their entirety as charges to interest expense on the Consolidated Statements of Income.
[3]	Income tax reclassifications related to commodity cash flow hedge amounts are included in their entirety as charges to income taxes on the Consolidated Statements of Income.
[4]	Income tax reclassifications related to interest rate cash flow hedge amounts are included in their entirety as credits to income taxes on the Consolidated Statements of Income.

Asset Retirement Obligations (

Asset Retirement Obligations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at beginning of year	$ 67.6	$ 69.3
Accretion	1	0.8
Liabilities incurred	0.2	0.1
Revisions in estimated cash flows	2.1	5.7
Liabilities settled	(0.4)	(0.9)
AROs at end of period	$ 70.5	$ 75

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Abandonment and impairment	$ 0.2	$ 0	$ 12.7		$ 2
Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	0.4	4.8	0.4	$ 25	4.8
Long-term investment	15.1	16.2	15.1	14.1	16.2
Financial liabilities [Abstract]
Short-term debt	458.5	214	458.5	457.6	214
Long-term debt, including current portion	957	1,231.8	957	1,206.7	1,231.8
Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0.4	4.8	0.4	25	4.8
Financial liabilities [Abstract]
Short-term debt	458.5	214	458.5	457.6	214
Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial liabilities [Abstract]
Long-term debt, including current portion	1,050.4	1,396.3	1,050.4	1,263.7	1,396.3
Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Long-term investment	15.1	16.2	15.1	14.1	16.2
Wexpro [Member]
Fair Value Disclosures [Abstract]
Abandonment and impairment				12.1
Questar Gas [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0	0	10.5	0
Financial liabilities [Abstract]
Checks outstanding in excess of cash balances	0.7	0.4	0.7	0	0.4
Notes payable to Questar	140.5	35.8	140.5	273.3	35.8
Long-term debt, including current portion	527.6	526.8	527.6	527.4	526.8
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0	0	10.5	0
Financial liabilities [Abstract]
Checks outstanding in excess of cash balances	0.7	0.4	0.7	0	0.4
Notes payable to Questar	140.5	35.8	140.5	273.3	35.8
Questar Gas [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial liabilities [Abstract]
Long-term debt, including current portion	591.7	629	591.7	568.4	629
Questar Pipeline [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Cash and cash equivalents	1.2	6.1	1.2	10.2	6.1
Notes receivable from Questar	33.2	35.9	33.2	6	35.9
Financial liabilities [Abstract]
Long-term debt, including current portion	429.4	453.9	429.4	429.2	453.9
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	1.2	6.1	1.2	10.2	6.1
Notes receivable from Questar	33.2	35.9	33.2	6	35.9
Questar Pipeline [Member] | Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial liabilities [Abstract]
Long-term debt, including current portion	$ 458.7	$ 515.1	$ 458.7	$ 445.2	$ 515.1

Derivatives and Hedging (Detail

Derivatives and Hedging (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2015	Mar. 31, 2015
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ (0.4)			$ (0.2)	$ 0
Cash Flow Hedging [Member] | Questar Pipeline [Member] | Forward Starting Interest Rate Swaps Terminating Q4 2011 [Member]
Derivative [Line Items]
Notional amount		$ 150	$ 150
Debt Instrument, Face Amount		180	$ 180
Interest payment for terminated derivative instrument		$ 37.3
Life of long-term debt associated with cash flow hedges			30 years
Date Through Which Reclassifications Into Earnings From AOCI Will Take Place	2,041
Pre-tax net losses expected to be reclassified from AOCI to Consolidated statement of income	$ 0.5
Reclassification from accumulated OCI to income, time to transfer	12 months

Operations by Line of Busines35

Operations by Line of Business (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016USD ($)lines_of_business	Mar. 31, 2015USD ($)	Mar. 31, 2016USD ($)	Mar. 31, 2015USD ($)
Segment Reporting Information [Line Items]
Number of principal complementary lines of business | lines_of_business	3
Revenues by Line of Business	$ 456.3	$ 428.6	$ 1,162.6	$ 1,161
Operating Income (Loss)	135.7	147	363.1	404.1
Net Income (Loss)	78.5	84.6	202.6	226
Questar Gas [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	407.9	374.8	950.7	939.4
Operating Income (Loss)	83.4	76.6	129.4	116.3
Net Income (Loss)	47.6	43.8	68.1	59.4
Wexpro [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	3.5	6.3	20.1	29.6
Operating Income (Loss)	39.7	41.7	145.4	176.5
Net Income (Loss)	26.2	27.7	97.4	118.7
Questar Pipeline [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	43	46.8	184.1	189
Operating Income (Loss)	27.6	27.4	114.6	114.9
Net Income (Loss)	14.2	13.9	59.9	58.8
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	1.9	0.7	7.7	3
Operating Income (Loss)	(15)	1.3	(26.3)	(3.6)
Net Income (Loss)	(9.5)	(0.8)	(22.8)	(10.9)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	99.1	104.2	389.1	419.8
Intersegment Eliminations [Member] | Wexpro [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	79.8	84.8	314.1	346
Intersegment Eliminations [Member] | Questar Pipeline [Member]
Segment Reporting Information [Line Items]
Revenues by Line of Business	$ 19.3	$ 19.4	$ 75	$ 73.8

Employee Benefits (Details)

Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Qualified and nonqualified pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3.4	$ 13.4	$ 12.2
Interest cost	8.2	8.1	32.8	33.1
Expected return on plan assets	(12.2)	(11.6)	(48.3)	(44.6)
Prior service cost	0	0	0.1	0.5
Recognized net actuarial loss	3.8	5.7	20	17.2
Pension settlement costs	0	0	16.7	0
Net benefit cost	2.8	5.6	34.7	18.4
Estimated qualified pension plan cost for current fiscal year	8.2		8.2
Estimated nonqualified pension plan cost for current fiscal year	3		3
Postretirement benefits plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.2	0.5	0.6
Interest cost	0.9	0.9	3.5	3.7
Expected return on plan assets	(0.7)	(0.8)	(3.1)	(3)
Recognized net actuarial loss	0.2	0.3	1.1	0.7
Accretion of regulatory liability	0.2	0.2	1	0.8
Net benefit cost	0.7	$ 0.8	3	$ 2.8
Estimated postretirement benefits cost for current fiscal year, before accretion of regulatory liability	$ 2.1		$ 2.1

Contingencies (Details)

Contingencies (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)$ / shares	Apr. 25, 2016lawsuit
Loss Contingencies [Line Items]
Business Acquisition, Date of Acquisition Agreement	Jan. 31, 2016
Business Acquisition, Share Price | $ / shares	$ 25
Subsequent Event [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number		6
Subsequent Event [Member] | Pending Litigation, Third District Court, Salt Lake County, Utah [Member]
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number		4
Subsequent Event [Member] | Pending Litigation, United States District Court of Utah, Central Division [Member]
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number		2
Wexpro [Member]
Loss Contingencies [Line Items]
Overriding royalty interest	4.00%
Loss Contingency, Range of Possible Loss, Maximum | $	$ 14.1
Unaffiliated Entity [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Maximum | $	$ 16.2

Asset Impairments (Details)

Asset Impairments (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Property, Plant and Equipment [Line Items]
Abandonment and impairment	$ 0.2	$ 0	$ 12.7		$ 2
Wexpro [Member]
Property, Plant and Equipment [Line Items]
Abandonment and impairment				$ 12.1