CONSOLIDATED STATEMENTS OF INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 130.2	$ 164.0	$ 496.2	$ 577.9	$ 883.8	$ 970.4
Wexpro	8.1	8.4	17.3	16.2	32.6	30.3
Questar Pipeline / Revenues from unaffiliated customers	50.1	50.5	100.6	98.8	199.2	200.1
Total Revenues	188.4	222.9	614.1	692.9	1,115.6	1,200.8
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	(11.5)	31.2	141.2	241.1	221.6	345.3
Operating and maintenance	39.7	39.8	96.4	91.2	181.1	175.9
General and administrative	29.9	26.2	59.0	59.2	117.7	116.5
Production and other taxes	12.6	13.1	26.9	26.7	52.7	49.5
Depreciation, depletion and amortization	45.5	38.9	89.7	78.3	171.3	155.4
Total Operating Expenses	116.2	149.2	413.2	496.5	744.4	842.6
Net gain (loss) from asset sales	0.4	0	2.6	0.1	2.7	0.5
OPERATING INCOME	72.6	73.7	203.5	196.5	373.9	358.7
Interest and other income	2.6	2.3	4.0	5.2	9.2	11.5
Income from unconsolidated affiliate	0.9	1.0	1.8	1.9	3.7	3.8
Interest expense	(15.1)	(14.8)	(29.8)	(30.8)	(55.8)	(59.6)
Income Before Income Taxes	61.0	62.2	179.5	172.8	331.0	314.4
Income taxes	(21.8)	(21.9)	(65.1)	(62.6)	(118.9)	(112.8)
NET INCOME	39.2	40.3	114.4	110.2	212.1	201.6
Earnings Per Common Share
Basic	$ 0.22	$ 0.22	$ 0.64	$ 0.62	$ 1.19	$ 1.13
Diluted	$ 0.22	$ 0.22	$ 0.64	$ 0.62	$ 1.19	$ 1.13
Weighted-average common shares outstanding
Used in basic calculation	177.2	177.5	177.8	177.2	177.7	177.0
Used in diluted calculation	178.3	178.8	178.9	178.7	178.9	179.0
Dividends per common share (in dollars per share)	$ 0.1625	$ 0.1525	$ 0.325	$ 0.305	$ 0.64	$ 0.585
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	130.2	164.0	496.2	577.9	883.8	970.4
Revenues from affiliated company	1.0	1.0	1.8	1.8	3.3	2.5
Total Revenues	131.2	165.0	498.0	579.7	887.1	972.9
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	75.5	109.8	311.7	398.5	558.9	657.2
Operating and maintenance	24.9	24.4	65.8	61.8	122.5	112.7
General and administrative	12.7	10.2	24.4	24.8	50.6	51.9
Depreciation and amortization	11.8	10.9	23.6	21.8	46.3	43.2
Other taxes	4.8	4.0	9.2	8.3	15.9	14.5
Total Operating Expenses	129.7	159.3	434.7	515.2	794.2	879.5
OPERATING INCOME	1.5	5.7	63.3	64.5	92.9	93.4
Interest and other income	1.2	1.3	2.4	2.9	4.9	6.4
Interest expense	(6.5)	(6.5)	(13.3)	(13.1)	(26.1)	(26.0)
Income Before Income Taxes	(3.8)	0.5	52.4	54.3	71.7	73.8
Income taxes	1.5	(0.1)	(19.8)	(20.5)	(26.8)	(27.0)
NET INCOME	(2.3)	0.4	32.6	33.8	44.9	46.8
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	50.1	50.5	100.6	98.8	199.2	200.1
Revenues from affiliated companies	18.3	18.7	36.8	37.3	73.9	74.0
Total Revenues	68.4	69.2	137.4	136.1	273.1	274.1
OPERATING EXPENSES
Operating and maintenance	8.7	10.3	17.3	18.9	33.7	42.2
General and administrative	12.4	11.1	24.5	24.2	46.8	44.2
Depreciation and amortization	13.5	12.8	27.0	25.1	53.1	48.9
Other taxes	2.4	2.3	4.9	5.4	9.6	9.6
Cost of goods sold (excluding operating expenses shown separately)	0.7	1.0	1.2	1.6	2.7	3.0
Total Operating Expenses	37.7	37.5	74.9	75.2	145.9	147.9
Net gain (loss) from asset sales	0.1	0	0.1	0.1	0.3	0.8
OPERATING INCOME	30.8	31.7	62.6	61.0	127.5	127.0
Interest and other income	0.3	0.1	0.3	1.0	0.2	1.1
Income from unconsolidated affiliate	0.9	1.0	1.8	1.9	3.7	3.8
Interest expense	(6.6)	(6.8)	(13.2)	(13.9)	(23.8)	(28.0)
Income Before Income Taxes	25.4	26.0	51.5	50.0	107.6	103.9
Income taxes	(9.3)	(9.4)	(18.8)	(18.1)	(38.9)	(37.7)
NET INCOME	$ 16.1	$ 16.6	$ 32.7	$ 31.9	$ 68.7	$ 66.2