CONSOLIDATED STATEMENTS OF INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 89.4	$ 82.5	$ 647.8	$ 578.7	$ 928.8	$ 876.5
Wexpro	13.2	9.8	32.0	27.1	41.0	35.5
Questar Pipeline / Revenues from unaffiliated customers	47.0	49.5	142.3	150.1	195.3	198.7
Total Revenues	149.6	141.8	822.1	755.9	1,165.1	1,110.7
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	(35.0)	(42.1)	157.4	99.1	250.6	209.5
Operating and maintenance	36.4	36.8	122.2	133.2	169.8	182.5
General and administrative	24.4	29.0	90.2	88.0	123.0	122.6
Retirement incentive	0	0	0	0	4.9	0
Production and other taxes	15.2	11.1	45.2	38.0	55.1	50.3
Depreciation, depletion and amortization	47.4	45.9	143.4	135.6	189.4	177.1
Asset impairment	80.6	0	80.6	0	80.6	0
Total Operating Expenses	169.0	80.7	639.0	493.9	873.4	742.0
Net gain (loss) from asset sales	0	2.5	0.1	5.1	0.1	5.0
OPERATING INCOME (LOSS)	(19.4)	63.6	183.2	267.1	291.8	373.7
Interest and other income	3.1	1.7	9.2	5.7	10.5	7.2
Income from unconsolidated affiliate	0.9	1.0	2.8	2.8	3.7	3.7
Interest expense	(13.9)	(14.5)	(42.7)	(44.3)	(56.3)	(57.0)
INCOME (LOSS) BEFORE INCOME TAXES	(29.3)	51.8	152.5	231.3	249.7	327.6
Income taxes	10.1	(18.0)	(59.4)	(83.1)	(92.8)	(117.8)
NET INCOME (LOSS)	(19.2)	33.8	93.1	148.2	156.9	209.8
Earnings (Loss) Per Common Share
Basic	$ (0.11)	$ 0.20	$ 0.53	$ 0.84	$ 0.89	$ 1.18
Diluted	$ (0.11)	$ 0.19	$ 0.53	$ 0.83	$ 0.89	$ 1.18
Weighted-average common shares outstanding
Used in basic calculation	175.5	175.4	175.4	177.0	175.5	177.2
Used in diluted calculation	175.5	176.5	176.1	178.1	176.1	178.3
Dividends per common share (in dollars per share)	$ 0.18	$ 0.17	$ 0.53	$ 0.495	$ 0.70	$ 0.6575
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	89.4	82.5	647.8	578.7	928.8	876.5
Revenues from affiliated company	0.2	0.5	0.6	2.3	0.8	3.4
Total Revenues	89.6	83.0	648.4	581.0	929.6	879.9
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	50.1	44.7	424.2	356.4	601.1	551.6
Operating and maintenance	20.9	21.4	78.1	87.2	109.9	123.1
General and administrative	12.1	12.1	38.5	36.5	53.2	52.6
Retirement incentive	0	0	0	0	2.4	0
Depreciation and amortization	12.4	11.4	36.9	35.0	49.1	46.6
Other taxes	5.3	4.1	15.4	13.3	18.3	15.9
Total Operating Expenses	100.8	93.7	593.1	528.4	834.0	789.8
OPERATING INCOME (LOSS)	(11.2)	(10.7)	55.3	52.6	95.6	90.1
Interest and other income	1.3	1.4	3.8	3.8	5.5	4.9
Interest expense	(5.3)	(5.8)	(16.7)	(19.1)	(21.7)	(25.5)
INCOME (LOSS) BEFORE INCOME TAXES	(15.2)	(15.1)	42.4	37.3	79.4	69.5
Income taxes	6.2	5.8	(15.6)	(14.0)	(28.8)	(26.0)
NET INCOME (LOSS)	(9.0)	(9.3)	26.8	23.3	50.6	43.5
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	47.0	49.5	142.3	150.1	195.3	198.7
Revenues from affiliated companies	17.6	18.4	54.8	55.2	74.0	73.8
Total Revenues	64.6	67.9	197.1	205.3	269.3	272.5
OPERATING EXPENSES
Operating and maintenance	8.8	9.1	23.2	26.4	32.0	33.6
General and administrative	10.8	12.0	35.3	36.5	48.8	49.3
Retirement incentive	0	0	0	0	0.9	0
Depreciation and amortization	14.0	13.6	42.2	40.6	55.9	53.9
Asset impairment	80.6	0	80.6	0	80.6	0
Other taxes	2.5	2.4	7.4	7.3	9.2	9.4
Cost of sales (excluding operating expenses shown separately)	0.5	0.7	2.7	1.9	7.5	2.7
Total Operating Expenses	117.2	37.8	191.4	112.7	234.9	148.9
Net gain (loss) from asset sales	0	2.5	0	2.6	0.1	2.6
OPERATING INCOME (LOSS)	(52.6)	32.6	5.7	95.2	34.5	126.2
Interest and other income	0.6	0	1.2	0.3	1.5	0
Income from unconsolidated affiliate	0.9	1.0	2.8	2.8	3.7	3.7
Interest expense	(6.5)	(6.6)	(19.5)	(19.8)	(26.0)	(24.8)
INCOME (LOSS) BEFORE INCOME TAXES	(57.6)	27.0	(9.8)	78.5	13.7	105.1
Income taxes	19.7	(9.9)	2.2	(28.7)	(6.4)	(38.1)
NET INCOME (LOSS)	$ (37.9)	$ 17.1	$ (7.6)	$ 49.8	$ 7.3	$ 67.0