CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
REVENUES
Questar Gas / Revenues	$ 128.2	$ 141.7	$ 536.1	$ 516.5	$ 937.2	$ 936.1
Wexpro	1.9	10.1	5.4	16.4	11.9	31.9
Questar Pipeline / Revenues from unaffiliated customers	42.9	46.5	85.9	93.3	180.5	187.4
Other	1.1	1.0	3.0	1.7	7.8	3.6
Total Revenues	174.1	199.3	630.4	627.9	1,137.4	1,159.0
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	(27.7)	(9.0)	130.8	122.8	183.2	185.2
Operating and maintenance	39.9	40.5	90.3	92.8	179.1	187.6
General and administrative	26.0	27.4	55.6	56.8	107.8	120.0
Pension settlement costs	0.0	0.0	0.0	0.0	16.7	0.0
Merger and restructuring costs	3.7	0.0	18.3	0.0	18.3	0.0
Production and other taxes	11.4	12.8	23.1	26.6	47.8	56.2
Depreciation, depletion and amortization	56.4	53.6	112.3	107.9	220.4	209.5
Abandonment and impairment	0.1	0.1	0.3	0.1	12.7	0.1
Total Operating Expenses	109.8	125.4	430.7	407.0	786.0	758.6
Net gain (loss) from asset sales	0.1	1.4	0.4	1.4	0.8	2.5
OPERATING INCOME	64.4	75.3	200.1	222.3	352.2	402.9
Interest and other income	1.1	1.5	2.1	2.9	3.4	6.5
Income from unconsolidated affiliate	0.9	1.0	1.9	1.9	3.7	3.6
Interest expense	(15.5)	(15.8)	(31.3)	(31.7)	(62.6)	(63.2)
INCOME (LOSS) BEFORE INCOME TAXES	50.9	62.0	172.8	195.4	296.7	349.8
Income taxes	(17.8)	(21.4)	(61.2)	(70.2)	(101.6)	(123.5)
NET INCOME (LOSS)	$ 33.1	$ 40.6	$ 111.6	$ 125.2	$ 195.1	$ 226.3
Earnings Per Common Share
Basic (usd per share)	$ 0.19	$ 0.23	$ 0.64	$ 0.71	$ 1.11	$ 1.29
Diluted (usd per share)	$ 0.19	$ 0.23	$ 0.64	$ 0.71	$ 1.11	$ 1.28
Weighted-average common shares outstanding
Used in basic calculation (in shares)	176.0	176.4	175.9	176.3	175.9	176.1
Used in diluted calculation (in shares)	176.2	176.6	176.2	176.5	176.1	176.4
Dividends per common share (usd per share)	$ 0.22	$ 0.21	$ 0.44	$ 0.42	$ 0.86	$ 0.80
Questar Gas [Member]
REVENUES
Total Revenues	$ 128.2	$ 141.7	$ 536.1	$ 516.5	$ 937.2	$ 936.1
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	67.8	84.0	324.7	317.6	565.2	580.6
Operating and maintenance	24.9	24.8	59.5	57.9	113.5	114.3
General and administrative	11.4	12.8	24.4	26.2	48.8	52.3
Depreciation and amortization	15.0	13.6	29.7	27.1	57.7	53.9
Other taxes	5.3	5.1	10.6	9.7	20.2	17.6
Total Operating Expenses	124.4	140.3	448.9	438.5	805.4	818.7
OPERATING INCOME	3.8	1.4	87.2	78.0	131.8	117.4
Interest and other income	0.9	1.2	1.9	2.3	4.4	5.6
Interest expense	(7.5)	(7.1)	(15.2)	(14.2)	(29.3)	(28.3)
INCOME (LOSS) BEFORE INCOME TAXES	(2.8)	(4.5)	73.9	66.1	106.9	94.7
Income taxes	1.2	1.7	(27.9)	(25.1)	(37.6)	(34.8)
NET INCOME (LOSS)	(1.6)	(2.8)	46.0	41.0	69.3	59.9
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	42.9	46.5	85.9	93.3	180.5	187.4
Revenues from affiliated companies	17.5	17.8	36.8	37.2	74.7	73.9
Total Revenues	60.4	64.3	122.7	130.5	255.2	261.3
OPERATING EXPENSES
Operating and maintenance	9.0	8.9	17.6	19.0	36.2	39.8
General and administrative	8.9	10.5	19.2	21.0	37.1	40.1
Depreciation and amortization	13.7	13.7	27.4	27.7	54.3	55.0
Other taxes	2.2	2.1	4.5	4.4	8.9	8.8
Cost of sales (excluding operating expenses shown separately)	0.3	(0.2)	0.4	1.7	7.6	3.3
Total Operating Expenses	34.1	35.0	69.1	73.8	144.1	147.0
Net gain (loss) from asset sales	0.1	0.0	0.4	0.0	0.6	(0.5)
OPERATING INCOME	26.4	29.3	54.0	56.7	111.7	113.8
Interest and other income	0.2	0.2	0.3	0.4	0.8	1.2
Income from unconsolidated affiliate	0.9	1.0	1.9	1.9	3.7	3.6
Interest expense	(6.2)	(6.5)	(12.4)	(13.1)	(25.3)	(26.1)
INCOME (LOSS) BEFORE INCOME TAXES	21.3	24.0	43.8	45.9	90.9	92.5
Income taxes	(7.7)	(8.8)	(16.0)	(16.8)	(32.6)	(34.2)
NET INCOME (LOSS)	$ 13.6	$ 15.2	$ 27.8	$ 29.1	$ 58.3	$ 58.3