CONSOLIDATED STATEMENTS OF INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 418.3	$ 366.0	$ 912.0	$ 917.6
Wexpro	10.3	9.2	37.2	32.9
Questar Pipeline / Revenues from unaffiliated customers	48.3	50.5	200.9	199.6
Total Revenues	476.9	425.7	1,150.1	1,150.1
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	199.7	152.7	239.3	264.3
Operating and maintenance	48.2	56.7	172.3	181.2
General and administrative	33.8	29.1	125.5	114.0
Retirement incentive	0	0	4.9	0
Production and other taxes	15.3	14.3	48.9	53.2
Depreciation, depletion and amortization	48.5	44.2	185.9	164.7
Total Operating Expenses	345.5	297.0	776.8	777.4
Net gain (loss) from asset sales	0	2.2	2.9	2.3
OPERATING INCOME	131.4	130.9	376.2	375.0
Interest and other income	3.0	1.4	8.6	8.9
Income from unconsolidated affiliate	0.9	0.9	3.7	3.8
Interest expense	(14.5)	(14.7)	(57.7)	(55.5)
INCOME BEFORE INCOME TAXES	120.8	118.5	330.8	332.2
Income taxes	(47.9)	(43.3)	(121.1)	(119.0)
NET INCOME	72.9	75.2	209.7	213.2
Earnings Per Common Share
Basic	$ 0.42	$ 0.42	$ 1.20	$ 1.19
Diluted	$ 0.41	$ 0.42	$ 1.19	$ 1.19
Weighted-average common shares outstanding
Used in basic calculation	175.3	178.2	175.6	177.8
Used in diluted calculation	176.1	179.3	176.5	179.1
Dividends per common share (in dollars per share)	$ 0.17	$ 0.1625	$ 0.6725	$ 0.63
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	418.3	366.0	912.0	917.6
Revenues from affiliated company	0.3	0.8	2.0	3.3
Total Revenues	418.6	366.8	914.0	920.9
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	290.6	236.2	587.7	593.2
Operating and maintenance	33.7	40.9	111.8	122.0
General and administrative	12.7	11.7	52.2	48.1
Retirement incentive	0	0	2.4	0
Depreciation and amortization	12.1	11.8	47.5	45.4
Other taxes	5.2	4.4	17.0	15.1
Total Operating Expenses	354.3	305.0	818.6	823.8
OPERATING INCOME	64.3	61.8	95.4	97.1
Interest and other income	1.2	1.2	5.5	5.0
Interest expense	(5.8)	(6.8)	(23.1)	(26.1)
INCOME BEFORE INCOME TAXES	59.7	56.2	77.8	76.0
Income taxes	(22.7)	(21.3)	(28.6)	(28.4)
NET INCOME	37.0	34.9	49.2	47.6
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	48.3	50.5	200.9	199.6
Revenues from affiliated companies	19.5	18.5	75.4	74.3
Total Revenues	67.8	69.0	276.3	273.9
OPERATING EXPENSES
Operating and maintenance	7.4	8.6	34.0	35.3
General and administrative	12.4	12.1	50.3	45.5
Retirement incentive	0	0	0.9	0
Depreciation and amortization	14.1	13.5	54.9	52.4
Other taxes	2.5	2.5	9.1	9.5
Cost of sales (excluding operating expenses shown separately)	1.2	0.5	7.4	3.0
Total Operating Expenses	37.6	37.2	156.6	145.7
Net gain (loss) from asset sales	0	0	2.7	0.2
OPERATING INCOME	30.2	31.8	122.4	128.4
Interest and other income	0.3	0	0.9	0
Income from unconsolidated affiliate	0.9	0.9	3.7	3.8
Interest expense	(6.5)	(6.6)	(26.2)	(24.0)
INCOME BEFORE INCOME TAXES	24.9	26.1	100.8	108.2
Income taxes	(9.1)	(9.5)	(36.9)	(39.0)
NET INCOME	$ 15.8	$ 16.6	$ 63.9	$ 69.2