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, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 82.5	$ 89.8	$ 578.7	$ 667.7	$ 876.5	$ 970.4
Wexpro	9.8	6.9	27.1	23.1	35.5	31.1
Questar Pipeline / Revenues from unaffiliated customers	49.5	50.0	150.1	148.8	198.7	200.8
Total Revenues	141.8	146.7	755.9	839.6	1,110.7	1,202.3
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	(42.1)	(30.0)	99.1	211.1	209.5	338.5
Operating and maintenance	36.8	35.4	133.2	126.6	182.5	174.5
General and administrative	29.0	24.1	88.0	83.3	122.6	113.4
Production and other taxes	11.1	13.5	38.0	40.2	50.3	51.1
Depreciation, depletion and amortization	45.9	40.1	135.6	118.4	177.1	157.3
Total Operating Expenses	80.7	83.1	493.9	579.6	742.0	834.8
Net gain (loss) from asset sales	2.5	0.2	5.1	0.3	5.0	0.6
OPERATING INCOME (LOSS)	63.6	63.8	267.1	260.3	373.7	368.1
Interest and other income	1.7	3.7	5.7	8.9	7.2	12.3
Income from unconsolidated affiliate	1.0	1.0	2.8	2.9	3.7	3.9
Interest expense	(14.5)	(13.3)	(44.3)	(44.1)	(57.0)	(58.8)
Income (Loss) Before Income Taxes	51.8	55.2	231.3	228.0	327.6	325.5
Income taxes	(18.0)	(19.1)	(83.1)	(81.7)	(117.8)	(115.5)
NET INCOME (LOSS)	33.8	36.1	148.2	146.3	209.8	210.0
Earnings Per Common Share
Basic	$ 0.20	$ 0.21	$ 0.84	$ 0.83	$ 1.18	$ 1.19
Diluted	$ 0.19	$ 0.20	$ 0.83	$ 0.82	$ 1.18	$ 1.17
Weighted-average common shares outstanding
Used in basic calculation	175.4	177.5	177.0	177.3	177.2	177.1
Used in diluted calculation	176.5	178.9	178.1	178.7	178.3	178.8
Dividends per common share (in dollars per share)	$ 0.17	$ 0.1525	$ 0.495	$ 0.4575	$ 0.6575	$ 0.5975
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	82.5	89.8	578.7	667.7	876.5	970.4
Revenues from affiliated company	0.5	0.4	2.3	2.2	3.4	2.7
Total Revenues	83.0	90.2	581.0	669.9	879.9	973.1
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	44.7	52.0	356.4	450.5	551.6	656.6
Operating and maintenance	21.4	20.8	87.2	82.6	123.1	112.6
General and administrative	12.1	10.1	36.5	34.9	52.6	49.5
Depreciation and amortization	11.4	11.1	35.0	32.9	46.6	43.5
Other taxes	4.1	4.1	13.3	12.4	15.9	15.1
Total Operating Expenses	93.7	98.1	528.4	613.3	789.8	877.3
OPERATING INCOME (LOSS)	(10.7)	(7.9)	52.6	56.6	90.1	95.8
Interest and other income	1.4	1.4	3.8	4.3	4.9	6.1
Interest expense	(5.8)	(6.4)	(19.1)	(19.5)	(25.5)	(26.2)
Income (Loss) Before Income Taxes	(15.1)	(12.9)	37.3	41.4	69.5	75.7
Income taxes	5.8	5.0	(14.0)	(15.5)	(26.0)	(27.7)
NET INCOME (LOSS)	(9.3)	(7.9)	23.3	25.9	43.5	48.0
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	49.5	50.0	150.1	148.8	198.7	200.8
Revenues from affiliated companies	18.4	18.5	55.2	55.8	73.8	74.3
Total Revenues	67.9	68.5	205.3	204.6	272.5	275.1
OPERATING EXPENSES
Operating and maintenance	9.1	9.2	26.4	28.1	33.6	40.2
General and administrative	12.0	9.5	36.5	33.7	49.3	43.8
Depreciation and amortization	13.6	12.8	40.6	37.9	53.9	49.9
Other taxes	2.4	2.6	7.3	8.0	9.4	10.0
Cost of goods sold (excluding operating expenses shown separately)	0.7	0.7	1.9	2.3	2.7	3.1
Total Operating Expenses	37.8	34.8	112.7	110.0	148.9	147.0
Net gain (loss) from asset sales	2.5	0.2	2.6	0.3	2.6	0.9
OPERATING INCOME (LOSS)	32.6	33.9	95.2	94.9	126.2	129.0
Interest and other income	0	0.2	0.3	1.2	0	1.3
Income from unconsolidated affiliate	1.0	1.0	2.8	2.9	3.7	3.9
Interest expense	(6.6)	(5.6)	(19.8)	(19.5)	(24.8)	(26.5)
Income (Loss) Before Income Taxes	27.0	29.5	78.5	79.5	105.1	107.7
Income taxes	(9.9)	(10.7)	(28.7)	(28.8)	(38.1)	(39.0)
NET INCOME (LOSS)	$ 17.1	$ 18.8	$ 49.8	$ 50.7	$ 67.0	$ 68.7