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	43.0	46.8	184.1	189.0
Other	1.9	0.7	7.7	3.0
Total Revenues	456.3	428.6	1,162.6	1,161.0
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	0.0	16.7	0.0
Merger and restructuring costs	14.6	0.0	14.6	0.0
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	0.0	12.7	2.0
Total Operating Expenses	320.9	281.6	801.6	758.1
Net gain (loss) from asset sales	0.3	0.0	2.1	1.2
OPERATING INCOME	135.7	147.0	363.1	404.1
Interest and other income	1.0	1.4	3.8	6.2
Income from unconsolidated affiliate	1.0	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	$ 226.0
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	176.0
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	13.0	13.4	50.2	52.4
Depreciation and amortization	14.7	13.5	56.3	53.9
Other taxes	5.3	4.6	20.0	17.3
Total Operating Expenses	324.5	298.2	821.3	823.2
Net gain (loss) from asset sales	0.0	0.0	0.0	0.1
OPERATING INCOME	83.4	76.6	129.4	116.3
Interest and other income	1.0	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	43.0	46.8	184.1	189.0
Revenues from affiliated companies	19.3	19.4	75.0	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	14.0	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	35.0	38.8	145.0	147.4
Net gain (loss) from asset sales	0.3	0.0	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	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)	(8.0)	(33.7)	(34.5)
NET INCOME	$ 14.2	$ 13.9	$ 59.9	$ 58.8