CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
OPERATING ACTIVITIES
Net income (loss)	$ 148.2	$ 146.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	141.3	125.5
Deferred income taxes	65.1	84.6
Share-based compensation	7.5	8.0
Net (gain) loss from asset sales	(5.1)	(0.3)
(Income) from unconsolidated affiliate	(2.8)	(2.9)
Distributions from unconsolidated affiliate and other	3.7	3.2
Changes in operating assets and liabilities	28.1	81.5
Net Cash Provided By Operating Activities	386.0	445.9
INVESTING ACTIVITIES
Property, plant and equipment	(276.1)	(255.2)
Cash used in disposition of assets	(2.5)	(1.8)
Proceeds from disposition of assets	4.5	0.3
Net Cash Used In Investing Activities	(274.1)	(256.7)
FINANCING ACTIVITIES
Common stock issued	4.7	6.4
Common stock repurchased	(72.5)	(3.8)
Change in short-term debt	44.0	36.0
Long-term debt and capital lease obligation repaid	(25.6)	(182.0)
Long-term debt issuance costs	0	(1.3)
Checks outstanding in excess of cash balances	5.4	9.6
Dividends paid	(87.6)	(81.2)
Tax benefits from share-based compensation	8.1	5.3
Net Cash Provided By (Used In) Financing Activities	(123.5)	(211.0)
Change in cash and cash equivalents	(11.6)	(21.8)
Beginning cash and cash equivalents	11.6	21.8
Ending cash and cash equivalents	0	0
Questar Gas [Member]
OPERATING ACTIVITIES
Net income (loss)	23.3	25.9
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	38.7	36.3
Deferred income taxes	20.6	18.0
Share-based compensation	0.9	0.8
Changes in operating assets and liabilities	17.6	73.2
Net Cash Provided By Operating Activities	101.1	154.2
INVESTING ACTIVITIES
Property, plant and equipment	(120.8)	(80.4)
Cash used in disposition of assets	(1.8)	(1.5)
Proceeds from disposition of assets	0.3	0.2
Net Cash Used In Investing Activities	(122.3)	(81.7)
FINANCING ACTIVITIES
Long-term debt and capital lease obligation repaid	(25.0)	(2.0)
Change in notes payable to Questar	63.9	(55.7)
Checks outstanding in excess of cash balances	2.0	3.2
Dividends paid	(24.7)	(22.7)
Net Cash Provided By (Used In) Financing Activities	16.2	(77.2)
Change in cash and cash equivalents	(5.0)	(4.7)
Beginning cash and cash equivalents	5.0	4.7
Ending cash and cash equivalents	0	0
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income (loss)	49.8	50.7
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	42.5	40.0
Deferred income taxes	5.0	29.3
Share-based compensation	1.5	1.4
Net (gain) loss from asset sales	(2.6)	(0.3)
(Income) from unconsolidated affiliate	(2.8)	(2.9)
Distributions from unconsolidated affiliate and other	3.7	3.2
Changes in operating assets and liabilities	18.5	0.1
Net Cash Provided By Operating Activities	115.6	121.5
INVESTING ACTIVITIES
Property, plant and equipment	(41.6)	(83.6)
Cash used in disposition of assets	(0.7)	(0.3)
Proceeds from disposition of assets	4.2	0.1
Net Cash Used In Investing Activities	(38.1)	(83.8)
FINANCING ACTIVITIES
Long-term debt and capital lease obligation repaid	0	(180.0)
Change in notes receivable from Questar	(33.2)	30.3
Change in notes payable to Questar	0	130.3
Dividends paid	(47.3)	(23.2)
Net Cash Provided By (Used In) Financing Activities	(80.5)	(42.6)
Change in cash and cash equivalents	(3.0)	(4.9)
Beginning cash and cash equivalents	3.4	5.3
Ending cash and cash equivalents	$ 0.4	$ 0.4