CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
OPERATING ACTIVITIES
Net income	$ 85.1	$ 72.9
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	57.2	50.2
Deferred income taxes	(1.2)	25.4
Asset impairment	0	0
Share-based compensation	3.2	3.1
(Income) from unconsolidated affiliate	(0.9)	(0.9)
Distributions from unconsolidated affiliate and other	1.6	1.5
Changes in operating assets and liabilities	67.9	53.8
Net Cash Provided By Operating Activities	212.9	206.0
INVESTING ACTIVITIES
Property, plant and equipment	(69.7)	(84.0)
Cash used in disposition of assets	(0.9)	(0.5)
Proceeds from disposition of assets	0	0.1
Net Cash Used In Investing Activities	(70.6)	(84.4)
FINANCING ACTIVITIES
Common stock issued	0.5	1.8
Common stock repurchased	(2.8)	(3.5)
Change in short-term debt	(119.0)	(61.0)
Long-term debt and capital lease obligation repaid	(0.3)	(40.1)
Dividends paid	(31.6)	(29.8)
Tax benefits from share-based compensation	0.5	1.4
Net Cash Provided By (Used In) Financing Activities	(152.7)	(131.2)
Change in cash and cash equivalents	(10.4)	(9.6)
Beginning cash and cash equivalents	16.0	16.8
Ending cash and cash equivalents	5.6	7.2
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	39.6	37.0
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.6	13.4
Deferred income taxes	(0.1)	10.7
Share-based compensation	0.3	0.4
Changes in operating assets and liabilities	45.3	44.0
Net Cash Provided By Operating Activities	99.7	105.5
INVESTING ACTIVITIES
Property, plant and equipment	(48.9)	(31.7)
Cash used in disposition of assets	(0.9)	(0.4)
Affiliated-company property, plant and equipment transfers	0	10.7
Net Cash Used In Investing Activities	(49.8)	(21.4)
FINANCING ACTIVITIES
Change in notes receivable from Questar	(30.6)	0
Change in notes payable to Questar	(17.7)	(33.8)
Long-term debt and capital lease obligation repaid	0	(40.0)
Dividends paid	(9.0)	(8.9)
Net Cash Provided By (Used In) Financing Activities	(57.3)	(82.7)
Change in cash and cash equivalents	(7.4)	1.4
Beginning cash and cash equivalents	8.8	1.4
Ending cash and cash equivalents	1.4	2.8
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	15.7	15.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.1	14.7
Deferred income taxes	(0.1)	3.2
Asset impairment	0	0
Share-based compensation	0.6	0.7
(Income) from unconsolidated affiliate	(0.9)	(0.9)
Distributions from unconsolidated affiliate and other	1.5	1.5
Changes in operating assets and liabilities	13.0	(1.4)
Net Cash Provided By Operating Activities	43.9	33.6
INVESTING ACTIVITIES
Property, plant and equipment	(8.5)	(14.1)
Cash used in disposition of assets	0	(0.1)
Affiliated-company property, plant and equipment transfers	0	(10.7)
Net Cash Used In Investing Activities	(8.5)	(24.9)
FINANCING ACTIVITIES
Change in notes receivable from Questar	(17.2)	5.6
Dividends paid	(16.0)	(16.0)
Net Cash Provided By (Used In) Financing Activities	(33.2)	(10.4)
Change in cash and cash equivalents	2.2	(1.7)
Beginning cash and cash equivalents	2.7	7.1
Ending cash and cash equivalents	$ 4.9	$ 5.4