CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
OPERATING ACTIVITIES
Net income	$ 157.8	$ 164.0
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	168.3	169.1
Deferred income taxes	16.5	1.4
Abandonment and impairment	0.1	2.0
Share-based compensation	8.7	8.5
Net (gain) from asset sales	(1.6)	(1.6)
(Income) from unconsolidated affiliate	(2.8)	(2.7)
Distributions from unconsolidated affiliate and other	3.9	4.1
Changes in operating assets and liabilities	13.1	17.7
Net Cash Provided By Operating Activities	364.0	362.5
INVESTING ACTIVITIES
Property, plant and equipment	(213.7)	(235.3)
Questar Gas acquisition of gas distribution system	(11.4)	0.0
Cash used in disposition of assets	(2.8)	(2.6)
Proceeds from disposition of assets	2.0	9.4
Net Cash Used In Investing Activities	(225.9)	(228.5)
FINANCING ACTIVITIES
Common stock issued	2.5	1.0
Common stock repurchased	(21.4)	(3.8)
Change in short-term debt	(42.0)	(42.0)
Checks outstanding in excess of cash balances	2.8	0.0
Capital lease obligation repaid	(1.0)	(0.7)
Dividends paid	(111.2)	(98.5)
Tax benefits from share-based compensation	0.2	1.3
Net Cash Used In Financing Activities	(170.1)	(142.7)
Change in cash and cash equivalents	(32.0)	(8.7)
Beginning cash and cash equivalents	32.0	16.0
Ending cash and cash equivalents	0.0	7.3
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	32.2	27.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	45.0	44.2
Deferred income taxes	18.0	7.7
Share-based compensation	1.0	1.0
Net (gain) from asset sales	0.0	(0.1)
Changes in operating assets and liabilities	24.1	2.6
Net Cash Provided By Operating Activities	120.3	82.6
INVESTING ACTIVITIES
Property, plant and equipment	(153.2)	(138.2)
Questar Gas acquisition of gas distribution system	(11.4)	0.0
Cash used in disposition of assets	(2.3)	(2.2)
Proceeds from disposition of assets	0.2	0.8
Net Cash Used In Investing Activities	(166.7)	(139.6)
FINANCING ACTIVITIES
Change in notes payable to Questar	60.7	73.1
Checks outstanding in excess of cash balances	3.4	2.1
Dividends paid to Questar	(37.5)	(27.0)
Net Cash Used In Financing Activities	26.6	48.2
Change in cash and cash equivalents	(19.8)	(8.8)
Beginning cash and cash equivalents	19.8	8.8
Ending cash and cash equivalents	0.0	0.0
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	44.3	46.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	42.8	42.5
Deferred income taxes	0.2	1.3
Share-based compensation	1.6	1.5
Net (gain) from asset sales	(0.1)	0.0
(Income) from unconsolidated affiliate	(2.8)	(2.7)
Distributions from unconsolidated affiliate and other	3.5	3.8
Changes in operating assets and liabilities	4.7	4.3
Net Cash Provided By Operating Activities	94.2	97.0
INVESTING ACTIVITIES
Property, plant and equipment	(28.0)	(45.3)
Cash used in disposition of assets	(0.5)	(0.4)
Proceeds from disposition of assets	0.1	0.2
Net Cash Used In Investing Activities	(28.4)	(45.5)
FINANCING ACTIVITIES
Change in notes receivable from Questar	(8.1)	(5.8)
Dividends paid to Questar	(64.0)	(48.0)
Net Cash Used In Financing Activities	(72.1)	(53.8)
Change in cash and cash equivalents	(6.3)	(2.3)
Beginning cash and cash equivalents	7.4	2.7
Ending cash and cash equivalents	$ 1.1	$ 0.4