CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
OPERATING ACTIVITIES
Net income	$ 114.4	$ 110.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	93.6	83.1
Deferred income taxes	60.6	58.5
Share-based compensation	5.2	5.9
Net (gain) loss from asset sales	(2.6)	(0.1)
(Income) from unconsolidated affiliate	(1.8)	(1.9)
Distributions from unconsolidated affiliate and other	2.2	2.4
Changes in operating assets and liabilities	33.4	111.3
Net Cash Provided By Operating Activities	305.0	369.4
INVESTING ACTIVITIES
Property, plant and equipment	(190.8)	(143.4)
Cash used in disposition of assets	(1.7)	(1.1)
Proceeds from disposition of assets	0.4	0.2
Net Cash Used In Investing Activities	(192.1)	(144.3)
FINANCING ACTIVITIES
Common stock issued	3.8	5.6
Common stock repurchased	(56.8)	(2.6)
Change in short-term debt	(29.0)	(105.0)
Long-term debt and capital lease obligation repaid	(0.4)	(100.0)
Checks outstanding in excess of cash balances	11.8	4.5
Dividends paid	(57.8)	(54.1)
Tax benefits from share-based compensation	3.9	4.7
Net Cash Provided By (Used In) Financing Activities	(124.5)	(246.9)
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	32.6	33.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	26.1	24.0
Deferred income taxes	0.8	20.4
Share-based compensation	0.6	0.6
Changes in operating assets and liabilities	73.9	94.4
Net Cash Provided By Operating Activities	134.0	173.2
INVESTING ACTIVITIES
Property, plant and equipment	(85.9)	(55.2)
Cash used in disposition of assets	(1.6)	(1.0)
Proceeds from disposition of assets	0.2	0.2
Net Cash Used In Investing Activities	(87.3)	(56.0)
FINANCING ACTIVITIES
Change in notes payable to Questar	(40.6)	(109.6)
Checks outstanding in excess of cash balances	5.4	2.9
Dividends paid	(16.5)	(15.2)
Net Cash Provided By (Used In) Financing Activities	(51.7)	(121.9)
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	32.7	31.9
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	28.3	26.6
Deferred income taxes	3.5	18.4
Share-based compensation	1.0	0.9
Net (gain) loss from asset sales	(0.1)	(0.1)
(Income) from unconsolidated affiliate	(1.8)	(1.9)
Distributions from unconsolidated affiliate and other	2.2	2.4
Changes in operating assets and liabilities	(2.2)	(6.5)
Net Cash Provided By Operating Activities	63.6	71.7
INVESTING ACTIVITIES
Property, plant and equipment	(25.3)	(40.9)
Cash used in disposition of assets	(0.1)	(0.1)
Proceeds from disposition of assets	0.2	0
Net Cash Used In Investing Activities	(25.2)	(41.0)
FINANCING ACTIVITIES
Long-term debt and capital lease obligation repaid	0	(100.0)
Change in notes receivable from Questar	(10.0)	30.3
Change in notes payable to Questar	0	49.3
Dividends paid	(31.5)	(15.4)
Net Cash Provided By (Used In) Financing Activities	(41.5)	(35.8)
Change in cash and cash equivalents	(3.1)	(5.1)
Beginning cash and cash equivalents	3.4	5.3
Ending cash and cash equivalents	$ 0.3	$ 0.2