CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 917.6	$ 960.9	$ 985.2
Wexpro	22.9	35.6	45.1
Questar Pipeline / Revenues from unaffiliated customers	187.9	190.2	189.5
Other	6.5	2.6	0.2
Total Revenues	1,134.9	1,189.3	1,220.0
OPERATING EXPENSES
Cost of sales (excluding operating expenses shown separately)	175.2	186.3	285.9
Cost of natural gas sold
Operating and maintenance	181.6	194.2	179.4
General and administrative	109.0	122.7	115.9
Pension settlement costs	16.7	0.0	0.0
Production and other taxes	51.3	66.2	57.4
Depreciation, depletion and amortization	216.0	213.7	194.8
Abandonment and impairment	12.5	2.0	80.6
Total Operating Expenses	762.3	785.1	914.0
Net gain (loss) from asset sales	1.8	1.2	(0.2)
OPERATING INCOME	374.4	405.4	305.8
Interest and other income	4.2	6.6	9.9
Income from unconsolidated affiliate	3.7	3.5	3.7
Interest expense	(63.0)	(63.1)	(56.9)
INCOME BEFORE INCOME TAXES	319.3	352.4	262.5
Income taxes	(110.6)	(125.9)	(101.3)
NET INCOME	$ 208.7	$ 226.5	$ 161.2
Earnings Per Common Share
Basic	$ 1.18	$ 1.29	$ 0.92
Diluted	$ 1.18	$ 1.29	$ 0.92
Weighted-average common shares outstanding
Used in basic calculation	176.1	175.8	175.4
Used in diluted calculation	176.3	176.1	176.0
Questar Gas [Member]
REVENUES
Questar Gas / Revenues from unaffiliated customers	$ 917.6	$ 960.9	$ 985.2
Revenues from affiliated company	0.0	0.0	0.6
Total Revenues	917.6	960.9	985.8
Cost of natural gas sold
Cost of natural gas sold - unaffiliated parties	164.6	181.4	279.7
Cost of natural gas sold - affiliated companies	393.5	423.4	370.9
Total cost of natural gas sold (excluding operating expenses shown separately) / Total Questar Gas cost of natural gas sold	558.1	604.8	650.6
Operating and maintenance	111.9	122.5	113.1
General and administrative	50.6	52.8	52.5
Depreciation and amortization	55.1	53.6	49.7
Other taxes	19.3	17.8	18.0
Total Operating Expenses	795.0	851.5	883.9
Net gain (loss) from asset sales	0.0	0.1	0.0
OPERATING INCOME	122.6	109.5	101.9
Interest and other income	4.8	5.9	5.1
Interest expense	(28.3)	(28.2)	(22.3)
INCOME BEFORE INCOME TAXES	99.1	87.2	84.7
Income taxes	(34.8)	(32.0)	(31.9)
NET INCOME	64.3	55.2	52.8
Questar Pipeline [Member]
REVENUES
Questar Pipeline / Revenues from unaffiliated customers	187.9	190.2	189.5
Revenues from affiliated companies	75.1	73.7	76.7
Total Revenues	263.0	263.9	266.2
Cost of natural gas sold
Operating and maintenance	37.6	39.3	37.6
General and administrative	38.9	38.9	41.6
Depreciation and amortization	54.6	54.5	55.5
Abandonment and impairment	0.0	0.0	80.6
Other taxes	8.8	9.1	9.3
Cost of sales (excluding operating expenses shown separately)	8.9	4.0	6.1
Total Operating Expenses	148.8	145.8	230.7
Net gain (loss) from asset sales	0.2	(0.5)	0.0
OPERATING INCOME	114.4	117.6	35.5
Interest and other income	0.9	1.2	1.8
Income from unconsolidated affiliate	3.7	3.5	3.7
Interest expense	(26.0)	(26.1)	(25.8)
INCOME BEFORE INCOME TAXES	93.0	96.2	15.2
Income taxes	(33.4)	(35.6)	(7.0)
NET INCOME	$ 59.6	$ 60.6	$ 8.2