CONSOLIDATED STATEMENTS OF INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 859.7	$ 965.5	$ 901.8
Wexpro	36.1	31.5	24.6
Questar Pipeline / Revenues from unaffiliated customers	203.1	197.4	197.2
Total Revenues	1,098.9	1,194.4	1,123.6
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	192.3	321.5	280.9
Cost of natural gas sold
Operating and maintenance	180.8	175.9	175.8
General and administrative	120.8	117.9	108.5
Retirement incentive	4.9	0	0
Separation costs	0	0	11.5
Production and other taxes	47.9	52.5	50.6
Depreciation, depletion and amortization	181.6	159.9	153.4
Total Operating Expenses	728.3	827.7	780.7
Net gain from asset sales	5.1	0.2	0.4
OPERATING INCOME	375.7	366.9	343.3
Interest and other income	7.0	10.4	11.7
Income from unconsolidated affiliate	3.7	3.8	3.8
Interest expense	(57.9)	(56.8)	(57.1)
Income From Continuing Operations Before Income Taxes	328.5	324.3	301.7
Income taxes	(116.5)	(116.4)	(109.4)
INCOME FROM CONTINUING OPERATIONS	212.0	207.9	192.3
Discontinued operations, net of income taxes	0	0	148.2
Discontinued operations, noncontrolling interest	0	0	(1.3)
Total Discontinued Operations, Net Of Income Taxes	0	0	146.9
NET INCOME ATTRIBUTABLE TO QUESTAR	212.0	207.9	339.2
Earnings Per Common Share Attributable To Questar
Basic from continuing operations	$ 1.20	$ 1.17	$ 1.09
Basic from discontinued operations	$ 0.00	$ 0.00	$ 0.84
Basic total	$ 1.20	$ 1.17	$ 1.93
Diluted from continuing operations	$ 1.19	$ 1.16	$ 1.08
Diluted from discontinued operations	$ 0.00	$ 0.00	$ 0.83
Diluted total	$ 1.19	$ 1.16	$ 1.91
Weighted-average common shares outstanding
Used in basic calculation	176.5	177.4	175.4
Used in diluted calculation	177.5	178.8	178.0
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	859.7	965.5	901.8
Revenues from affiliated company	2.5	3.3	1.1
Total Revenues	862.2	968.8	902.9
Cost of natural gas sold
Cost of natural gas sold / Unaffiliated parties	185.6	318.4	278.5
Cost of natural gas sold / Affiliated companies	347.7	327.3	313.7
Cost of natural gas sold (excluding operating expenses shown separately)	533.3	645.7	592.2
Operating and maintenance	119.0	118.5	114.4
General and administrative	51.2	51.0	49.9
Retirement incentive	2.4	0	0
Depreciation and amortization	47.2	44.5	43.7
Production and other taxes	16.2	15.0	14.1
Total Operating Expenses	769.3	874.7	814.3
OPERATING INCOME	92.9	94.1	88.6
Interest and other income	5.5	5.4	6.7
Interest expense	(24.1)	(25.9)	(26.2)
Income From Continuing Operations Before Income Taxes	74.3	73.6	69.1
Income taxes	(27.2)	(27.5)	(25.2)
NET INCOME ATTRIBUTABLE TO QUESTAR	47.1	46.1	43.9
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	203.1	197.4	197.2
Revenues from affiliated companies	74.4	74.4	74.0
Total Revenues	277.5	271.8	271.2
Cost of natural gas sold
Operating and maintenance	35.2	35.3	41.4
General and administrative	50.0	46.5	41.0
Retirement incentive	0.9	0	0
Depreciation and amortization	54.3	51.2	47.4
Production and other taxes	9.1	10.1	9.0
Cost of sales (excluding operating expenses shown separately)	6.7	3.1	2.4
Total Operating Expenses	156.2	146.2	141.2
Net gain from asset sales	2.7	0.3	0.8
OPERATING INCOME	124.0	125.9	130.8
Interest and other income	0.6	0.9	0.4
Income from unconsolidated affiliate	3.7	3.8	3.8
Interest expense	(26.3)	(24.5)	(28.8)
Income From Continuing Operations Before Income Taxes	102.0	106.1	106.2
Income taxes	(37.3)	(38.2)	(38.8)
NET INCOME ATTRIBUTABLE TO QUESTAR	$ 64.7	$ 67.9	$ 67.4