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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 140.1	$ 130.2	$ 558.4	$ 496.2	$ 921.9	$ 883.8
Wexpro	8.5	8.1	18.8	17.3	37.6	32.6
Questar Pipeline / Revenues from unaffiliated customers	47.0	50.1	95.3	100.6	197.8	199.2
Total Revenues	195.6	188.4	672.5	614.1	1,157.3	1,115.6
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	(7.3)	(11.5)	192.4	141.2	243.5	221.6
Operating and maintenance	37.6	39.7	85.8	96.4	170.2	181.1
General and administrative	32.0	29.9	65.8	59.0	127.6	117.7
Retirement incentive	0	0	0	0	4.9	0
Production and other taxes	14.7	12.6	30.0	26.9	51.0	52.7
Depreciation, depletion and amortization	47.5	45.5	96.0	89.7	187.9	171.3
Total Operating Expenses	124.5	116.2	470.0	413.2	785.1	744.4
Net gain (loss) from asset sales	0.1	0.4	0.1	2.6	2.6	2.7
OPERATING INCOME	71.2	72.6	202.6	203.5	374.8	373.9
Interest and other income	3.1	2.6	6.1	4.0	9.1	9.2
Income from unconsolidated affiliate	1.0	0.9	1.9	1.8	3.8	3.7
Interest expense	(14.3)	(15.1)	(28.8)	(29.8)	(56.9)	(55.8)
INCOME (LOSS) BEFORE INCOME TAXES	61.0	61.0	181.8	179.5	330.8	331.0
Income taxes	(21.6)	(21.8)	(69.5)	(65.1)	(120.9)	(118.9)
NET INCOME (LOSS)	39.4	39.2	112.3	114.4	209.9	212.1
Earnings Per Common Share
Basic	$ 0.22	$ 0.22	$ 0.64	$ 0.64	$ 1.20	$ 1.19
Diluted	$ 0.22	$ 0.22	$ 0.64	$ 0.64	$ 1.19	$ 1.19
Weighted-average common shares outstanding
Used in basic calculation	175.5	177.2	175.4	177.8	175.3	177.7
Used in diluted calculation	176.3	178.3	176.2	178.9	176.1	178.9
Dividends per common share (in dollars per share)	$ 0.18	$ 0.1625	$ 0.35	$ 0.325	$ 0.69	$ 0.64
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	140.1	130.2	558.4	496.2	921.9	883.8
Revenues from affiliated company	0.1	1.0	0.4	1.8	1.1	3.3
Total Revenues	140.2	131.2	558.8	498.0	923.0	887.1
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	83.5	75.5	374.1	311.7	595.7	558.9
Operating and maintenance	23.5	24.9	57.2	65.8	110.4	122.5
General and administrative	13.7	12.7	26.4	24.4	53.2	50.6
Retirement incentive	0	0			2.4	0
Depreciation and amortization	12.4	11.8	24.5	23.6	48.1	46.3
Other taxes	4.9	4.8	10.1	9.2	17.1	15.9
Total Operating Expenses	138.0	129.7	492.3	434.7	826.9	794.2
OPERATING INCOME	2.2	1.5	66.5	63.3	96.1	92.9
Interest and other income	1.3	1.2	2.5	2.4	5.6	4.9
Interest expense	(5.6)	(6.5)	(11.4)	(13.3)	(22.2)	(26.1)
INCOME (LOSS) BEFORE INCOME TAXES	(2.1)	(3.8)	57.6	52.4	79.5	71.7
Income taxes	0.9	1.5	(21.8)	(19.8)	(29.2)	(26.8)
NET INCOME (LOSS)	(1.2)	(2.3)	35.8	32.6	50.3	44.9
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	47.0	50.1	95.3	100.6	197.8	199.2
Revenues from affiliated companies	17.7	18.3	37.2	36.8	74.8	73.9
Total Revenues	64.7	68.4	132.5	137.4	272.6	273.1
OPERATING EXPENSES
Operating and maintenance	7.0	8.7	14.4	17.3	32.3	33.7
General and administrative	12.1	12.4	24.5	24.5	50.0	46.8
Retirement incentive	0	0			0.9	0
Depreciation and amortization	14.1	13.5	28.2	27.0	55.5	53.1
Other taxes	2.4	2.4	4.9	4.9	9.1	9.6
Cost of sales (excluding operating expenses shown separately)	1.0	0.7	2.2	1.2	7.7	2.7
Total Operating Expenses	36.6	37.7	74.2	74.9	155.5	145.9
Net gain (loss) from asset sales	0	0.1	0	0.1	2.6	0.3
OPERATING INCOME	28.1	30.8	58.3	62.6	119.7	127.5
Interest and other income	0.3	0.3	0.6	0.3	0.9	0.2
Income from unconsolidated affiliate	1.0	0.9	1.9	1.8	3.8	3.7
Interest expense	(6.5)	(6.6)	(13.0)	(13.2)	(26.1)	(23.8)
INCOME (LOSS) BEFORE INCOME TAXES	22.9	25.4	47.8	51.5	98.3	107.6
Income taxes	(8.4)	(9.3)	(17.5)	(18.8)	(36.0)	(38.9)
NET INCOME (LOSS)	$ 14.5	$ 16.1	$ 30.3	$ 32.7	$ 62.3	$ 68.7