CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
OPERATING ACTIVITIES
Net income	$ 75.2	$ 69.9
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	46.3	41.8
Deferred income taxes	39.6	31.3
Share-based compensation	2.7	3.5
Net (gain) loss from asset sales	(2.2)	(0.1)
(Income) from unconsolidated affiliate	(0.9)	(0.9)
Distributions from unconsolidated affiliate and other	1.3	1.0
Changes in operating assets and liabilities	58.7	82.3
Net Cash Provided By Operating Activities	220.7	228.8
INVESTING ACTIVITIES
Property, plant and equipment	(104.2)	(76.0)
Cash used in disposition of assets	(0.7)	(0.5)
Net Cash Used In Investing Activities	(104.9)	(76.5)
FINANCING ACTIVITIES
Common stock issued	2.8	5.6
Common stock repurchased	(6.6)	(2.3)
Change in short-term debt	(90.0)	(156.0)
Checks outstanding in excess of cash balances	0	1.6
Dividends paid	(29.0)	(27.0)
Tax benefits from share-based compensation	3.5	4.0
Net Cash Provided Used In Financing Activities	(119.3)	(174.1)
Change in cash and cash equivalents	(3.5)	(21.8)
Beginning cash and cash equivalents	11.6	21.8
Ending cash and cash equivalents	8.1	0
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	34.9	33.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	13.0	12.0
Deferred income taxes	(2.0)	6.0
Share-based compensation	0.3	0.3
Changes in operating assets and liabilities	83.3	67.5
Net Cash Provided By Operating Activities	129.5	119.2
INVESTING ACTIVITIES
Property, plant and equipment	(44.8)	(25.9)
Cash used in disposition of assets	(0.6)	(0.5)
Net Cash Used In Investing Activities	(45.4)	(26.4)
FINANCING ACTIVITIES
Change in notes payable to Questar	(76.3)	(89.5)
Dividends paid	(8.3)	(7.6)
Net Cash Provided Used In Financing Activities	(84.6)	(97.1)
Change in cash and cash equivalents	(0.5)	(4.3)
Beginning cash and cash equivalents	5.0	4.7
Ending cash and cash equivalents	4.5	0.4
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	16.6	15.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.0	13.1
Deferred income taxes	9.1	16.0
Share-based compensation	0.6	0.5
Net (gain) loss from asset sales	0	(0.1)
(Income) from unconsolidated affiliate	(0.9)	(0.9)
Distributions from unconsolidated affiliate and other	1.3	1.0
Changes in operating assets and liabilities	(5.9)	(5.5)
Net Cash Provided By Operating Activities	34.8	39.4
INVESTING ACTIVITIES
Property, plant and equipment	(12.1)	(25.7)
Cash used in disposition of assets	(0.1)	0
Net Cash Used In Investing Activities	(12.2)	(25.7)
FINANCING ACTIVITIES
Change in notes receivable from Questar	(5.7)	(10.4)
Dividends paid	(15.7)	(7.7)
Net Cash Provided Used In Financing Activities	(21.4)	(18.1)
Change in cash and cash equivalents	1.2	(4.4)
Beginning cash and cash equivalents	3.4	5.3
Ending cash and cash equivalents	$ 4.6	$ 0.9