CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 141.7	$ 145.0	$ 516.5	$ 541.3	$ 936.1	$ 968.1
Wexpro	10.1	7.8	16.4	20.1	31.9	46.4
Questar Pipeline / Revenues from unaffiliated customers	46.5	48.1	93.3	96.1	187.4	190.3
Other	1.0	0.4	1.7	0.7	3.6	0.9
Total Revenues	199.3	201.3	627.9	658.2	1,159.0	1,205.7
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	(9.0)	(24.3)	122.8	123.9	185.2	217.4
Operating and maintenance	40.5	42.5	92.8	99.4	187.6	190.3
General and administrative	27.4	29.2	56.8	59.5	120.0	112.3
Production and other taxes	12.8	18.7	26.6	36.6	56.2	64.0
Depreciation, depletion and amortization	53.6	56.8	107.9	112.1	209.5	210.9
Abandonment and impairment	0.1	2.0	0.1	2.0	0.1	82.6
Total Operating Expenses	125.4	124.9	407.0	433.5	758.6	877.5
Net gain (loss) from asset sales	1.4	0.1	1.4	0.1	2.5	(0.2)
OPERATING INCOME	75.3	76.5	222.3	224.8	402.9	328.0
Interest and other income	1.5	1.2	2.9	3.0	6.5	6.8
Income from unconsolidated affiliate	1.0	0.9	1.9	1.8	3.6	3.6
Interest expense	(15.8)	(15.8)	(31.7)	(31.6)	(63.2)	(59.7)
INCOME (LOSS) BEFORE INCOME TAXES	62.0	62.8	195.4	198.0	349.8	278.7
Income taxes	(21.4)	(22.5)	(70.2)	(72.6)	(123.5)	(104.4)
NET INCOME (LOSS)	$ 40.6	$ 40.3	$ 125.2	$ 125.4	$ 226.3	$ 174.3
Earnings Per Common Share
Basic	$ 0.23	$ 0.23	$ 0.71	$ 0.71	$ 1.29	$ 0.99
Diluted	$ 0.23	$ 0.23	$ 0.71	$ 0.71	$ 1.28	$ 0.99
Weighted-average common shares outstanding
Used in basic calculation	176.4	175.8	176.3	175.7	176.1	175.7
Used in diluted calculation	176.6	176.1	176.5	176.1	176.4	176.1
Dividends per common share	$ 0.21	$ 0.19	$ 0.42	$ 0.37	$ 0.80	$ 0.73
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 141.7	$ 145.0	$ 516.5	$ 541.3	$ 936.1	$ 968.1
Revenues from affiliated company	0.0	0.0	0.0	0.0	0.0	0.2
Total Revenues	141.7	145.0	516.5	541.3	936.1	968.3
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	84.0	87.2	317.6	341.8	580.6	618.3
Operating and maintenance	24.8	26.3	57.9	66.1	114.3	122.0
General and administrative	12.8	12.9	26.2	26.7	52.3	52.8
Depreciation and amortization	13.6	13.6	27.1	26.8	53.9	52.0
Other taxes	5.1	4.8	9.7	9.9	17.6	17.8
Total Operating Expenses	140.3	144.8	438.5	471.3	818.7	862.9
Net gain (loss) from asset sales	0.0	0.1	0.0	0.1	0.0	0.1
OPERATING INCOME	1.4	0.3	78.0	70.1	117.4	105.5
Interest and other income	1.2	1.3	2.3	2.6	5.6	5.2
Interest expense	(7.1)	(7.0)	(14.2)	(14.1)	(28.3)	(25.0)
INCOME (LOSS) BEFORE INCOME TAXES	(4.5)	(5.4)	66.1	58.6	94.7	85.7
Income taxes	1.7	2.1	(25.1)	(22.3)	(34.8)	(32.4)
NET INCOME (LOSS)	(2.8)	(3.3)	41.0	36.3	59.9	53.3
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	46.5	48.1	93.3	96.1	187.4	190.3
Revenues from affiliated companies	17.8	17.7	37.2	37.0	73.9	76.5
Total Revenues	64.3	65.8	130.5	133.1	261.3	266.8
OPERATING EXPENSES
Operating and maintenance	8.9	9.2	19.0	18.5	39.8	39.0
General and administrative	10.5	9.5	21.0	19.8	40.1	39.6
Depreciation and amortization	13.7	13.6	27.7	27.2	55.0	54.5
Abandonment and impairment	0.0	0.0	0.0	0.0	0.0	80.6
Other taxes	2.1	2.4	4.4	4.7	8.8	9.1
Cost of sales (excluding operating expenses shown separately)	(0.2)	0.7	1.7	2.4	3.3	6.3
Total Operating Expenses	35.0	35.4	73.8	72.6	147.0	229.1
Net gain (loss) from asset sales	0.0	0.0	0.0	0.0	(0.5)	0.0
OPERATING INCOME	29.3	30.4	56.7	60.5	113.8	37.7
Interest and other income	0.2	0.1	0.4	0.4	1.2	1.6
Income from unconsolidated affiliate	1.0	0.9	1.9	1.8	3.6	3.6
Interest expense	(6.5)	(6.6)	(13.1)	(13.1)	(26.1)	(25.9)
INCOME (LOSS) BEFORE INCOME TAXES	24.0	24.8	45.9	49.6	92.5	17.0
Income taxes	(8.8)	(9.1)	(16.8)	(18.2)	(34.2)	(7.7)
NET INCOME (LOSS)	$ 15.2	$ 15.7	$ 29.1	$ 31.4	$ 58.3	$ 9.3