CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
OPERATING ACTIVITIES
Net income (loss)	$ 164.0	$ 93.1
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	169.1	148.7
Deferred income taxes	1.4	37.2
Abandonment and impairment	2.0	80.6
Share-based compensation	8.5	7.7
Net (gain) loss from asset sales	(1.6)	(0.1)
(Income) from unconsolidated affiliate	(2.7)	(2.8)
Distributions from unconsolidated affiliate and other	4.1	4.2
Changes in operating assets and liabilities	17.7	55.4
Net Cash Provided By Operating Activities	362.5	424.0
INVESTING ACTIVITIES
Property, plant and equipment	(235.3)	(287.4)
Wexpro acquisition of producing properties	0	(106.7)
Cash used in disposition of assets	(2.6)	(3.1)
Proceeds from disposition of assets	9.4	0.6
Net Cash Used In Investing Activities	(228.5)	(396.6)
FINANCING ACTIVITIES
Common stock issued	1.0	2.2
Common stock repurchased	(3.8)	(4.2)
Change in short-term debt	(42.0)	92.0
Checks outstanding in excess of cash balances	0	1.6
Long-term debt and capital lease obligation repaid	(0.7)	(42.6)
Long-term debt issuance costs	0	(1.7)
Dividends paid	(98.5)	(93.0)
Tax benefits from share-based compensation	1.3	1.5
Net Cash Provided By (Used In) Financing Activities	(142.7)	(44.2)
Change in cash and cash equivalents	(8.7)	(16.8)
Beginning cash and cash equivalents	16.0	16.8
Ending cash and cash equivalents	7.3	0
Questar Gas [Member]
OPERATING ACTIVITIES
Net income (loss)	27.2	26.8
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	44.2	40.7
Deferred income taxes	7.7	29.1
Share-based compensation	1.0	1.1
Net (gain) loss from asset sales	(0.1)	0
Changes in operating assets and liabilities	2.6	49.9
Net Cash Provided By Operating Activities	82.6	147.6
INVESTING ACTIVITIES
Property, plant and equipment	(138.2)	(119.3)
Cash used in disposition of assets	(2.2)	(2.5)
Proceeds from disposition of assets	0.8	0.3
Affiliated-company property, plant and equipment transfers	0	10.8
Net Cash Used In Investing Activities	(139.6)	(110.7)
FINANCING ACTIVITIES
Change in notes payable to Questar	73.1	28.9
Checks outstanding in excess of cash balances	2.1	1.4
Long-term debt and capital lease obligation repaid	0	(42.0)
Dividends paid to Questar	(27.0)	(26.6)
Net Cash Provided By (Used In) Financing Activities	48.2	(38.3)
Change in cash and cash equivalents	(8.8)	(1.4)
Beginning cash and cash equivalents	8.8	1.4
Ending cash and cash equivalents	0	0
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income (loss)	46.3	(7.6)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	42.5	44.1
Deferred income taxes	1.3	(15.7)
Abandonment and impairment	0	80.6
Share-based compensation	1.5	1.6
(Income) from unconsolidated affiliate	(2.7)	(2.8)
Distributions from unconsolidated affiliate and other	3.8	3.9
Changes in operating assets and liabilities	4.3	3.6
Net Cash Provided By Operating Activities	97.0	107.7
INVESTING ACTIVITIES
Property, plant and equipment	(45.3)	(56.2)
Cash used in disposition of assets	(0.4)	(0.6)
Proceeds from disposition of assets	0.2	0.1
Affiliated-company property, plant and equipment transfers	0	(10.7)
Net Cash Used In Investing Activities	(45.5)	(67.4)
FINANCING ACTIVITIES
Change in notes receivable from Questar	(5.8)	2.1
Dividends paid to Questar	(48.0)	(48.0)
Net Cash Provided By (Used In) Financing Activities	(53.8)	(45.9)
Change in cash and cash equivalents	(2.3)	(5.6)
Beginning cash and cash equivalents	2.7	7.1
Ending cash and cash equivalents	$ 0.4	$ 1.5