CONSOLIDATED STATEMENTS OF INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 374.8	$ 396.3	$ 939.4	$ 963.2
Wexpro	6.3	12.3	29.6	47.1
Questar Pipeline / Revenues from unaffiliated customers	46.8	48.0	189.0	189.2
Other	0.7	0.3	3.0	0.5
Total Revenues	428.6	456.9	1,161.0	1,200.0
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	131.8	148.2	169.9	234.4
Operating and maintenance	52.3	56.9	189.6	186.7
General and administrative	29.4	30.3	121.8	113.8
Production and other taxes	13.8	17.9	62.1	60.0
Depreciation, depletion and amortization	54.3	55.3	212.7	201.6
Abandonment and impairment	0	0	2.0	80.6
Total Operating Expenses	281.6	308.6	758.1	877.1
Net gain (loss) from asset sales	0	0	1.2	(0.2)
OPERATING INCOME	147.0	148.3	404.1	322.7
Interest and other income	1.4	1.8	6.2	8.7
Income from unconsolidated affiliate	0.9	0.9	3.5	3.7
Interest expense	(15.9)	(15.8)	(63.2)	(58.2)
INCOME BEFORE INCOME TAXES	133.4	135.2	350.6	276.9
Income taxes	(48.8)	(50.1)	(124.6)	(103.5)
NET INCOME	84.6	85.1	226.0	173.4
Earnings Per Common Share
Basic	$ 0.48	$ 0.48	$ 1.29	$ 0.98
Diluted	$ 0.48	$ 0.48	$ 1.28	$ 0.98
Weighted-average common shares outstanding
Used in basic calculation	176.2	175.7	176.0	175.6
Used in diluted calculation	176.5	176.1	176.3	176.1
Dividends per common share	$ 0.21	$ 0.18	$ 0.78	$ 0.72
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	374.8	396.3	939.4	963.2
Revenues from affiliated company	0	0	0	0.3
Total Revenues	374.8	396.3	939.4	963.5
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	233.6	254.6	583.8	614.6
Operating and maintenance	33.1	39.8	115.8	119.2
General and administrative	13.4	13.8	52.4	53.6
Depreciation and amortization	13.5	13.2	53.9	50.8
Other taxes	4.6	5.1	17.3	17.9
Total Operating Expenses	298.2	326.5	823.2	856.1
Net gain (loss) from asset sales	0	0	0.1	0
OPERATING INCOME	76.6	69.8	116.3	107.4
Interest and other income	1.1	1.3	5.7	5.2
Interest expense	(7.1)	(7.1)	(28.2)	(23.6)
INCOME BEFORE INCOME TAXES	70.6	64.0	93.8	89.0
Income taxes	(26.8)	(24.4)	(34.4)	(33.6)
NET INCOME	43.8	39.6	59.4	55.4
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	46.8	48.0	189.0	189.2
Revenues from affiliated companies	19.4	19.3	73.8	76.5
Total Revenues	66.2	67.3	262.8	265.7
OPERATING EXPENSES
Operating and maintenance	10.1	9.3	40.1	38.1
General and administrative	10.5	10.3	39.1	40.9
Depreciation and amortization	14.0	13.6	54.9	55.0
Abandonment and impairment	0	0	0	80.6
Other taxes	2.3	2.3	9.1	9.1
Cost of sales (excluding operating expenses shown separately)	1.9	1.7	4.2	6.6
Total Operating Expenses	38.8	37.2	147.4	230.3
Net gain (loss) from asset sales	0	0	(0.5)	0
OPERATING INCOME	27.4	30.1	114.9	35.4
Interest and other income	0.2	0.3	1.1	1.8
Income from unconsolidated affiliate	0.9	0.9	3.5	3.7
Interest expense	(6.6)	(6.5)	(26.2)	(25.8)
INCOME BEFORE INCOME TAXES	21.9	24.8	93.3	15.1
Income taxes	(8.0)	(9.1)	(34.5)	(7.0)
NET INCOME	$ 13.9	$ 15.7	$ 58.8	$ 8.1