CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
OPERATING ACTIVITIES
Net income	$ 125.2	$ 125.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	111.3	116.4
Deferred income taxes	(7.2)	(4.6)
Abandonment and impairment	0.1	2.0
Share-based compensation	6.3	6.0
Net (gain) from asset sales	(1.4)	(0.1)
(Income) from unconsolidated affiliate	(1.9)	(1.8)
Distributions from unconsolidated affiliate and other	2.6	2.9
Changes in operating assets and liabilities	66.2	37.6
Net Cash Provided By Operating Activities	301.2	283.8
INVESTING ACTIVITIES
Property, plant and equipment	(127.3)	(134.4)
Questar Gas acquisition of gas distribution system	(11.4)	0.0
Cash used in disposition of assets	(1.8)	(1.7)
Proceeds from disposition of assets	1.1	0.8
Net Cash Used In Investing Activities	(139.4)	(135.3)
FINANCING ACTIVITIES
Common stock issued	1.5	1.0
Common stock repurchased	(4.1)	(2.9)
Change in short-term debt	(119.0)	(99.0)
Checks outstanding in excess of cash balances	2.5	0.9
Capital lease obligation repaid	(0.6)	(0.5)
Dividends paid	(74.1)	(65.0)
Tax benefits from share-based compensation	0.0	1.0
Net Cash Used In Financing Activities	(193.8)	(164.5)
Change in cash and cash equivalents	(32.0)	(16.0)
Beginning cash and cash equivalents	32.0	16.0
Ending cash and cash equivalents	0.0	0.0
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	41.0	36.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	29.9	29.4
Deferred income taxes	(1.8)	(0.2)
Share-based compensation	0.7	0.6
Net (gain) from asset sales	0.0	(0.1)
Changes in operating assets and liabilities	95.0	47.9
Net Cash Provided By Operating Activities	164.8	113.9
INVESTING ACTIVITIES
Property, plant and equipment	(88.3)	(87.8)
Questar Gas acquisition of gas distribution system	(11.4)	0.0
Cash used in disposition of assets	(1.4)	(1.4)
Proceeds from disposition of assets	0.1	0.4
Affiliated-company property, plant and equipment transfers	(0.1)	0.0
Net Cash Used In Investing Activities	(101.1)	(88.8)
FINANCING ACTIVITIES
Change in notes receivable from Questar	0.0	(3.0)
Change in notes payable to Questar	(59.6)	(17.7)
Checks outstanding in excess of cash balances	4.1	4.8
Dividends paid to Questar	(28.0)	(18.0)
Net Cash Used In Financing Activities	(83.5)	(33.9)
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	29.1	31.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	28.9	28.4
Deferred income taxes	(1.1)	(0.5)
Abandonment and impairment	0.0	0.0
Share-based compensation	1.3	1.0
Net (gain) from asset sales	0.0	0.0
(Income) from unconsolidated affiliate	(1.9)	(1.8)
Distributions from unconsolidated affiliate and other	2.4	2.7
Changes in operating assets and liabilities	(5.9)	16.2
Net Cash Provided By Operating Activities	52.8	77.4
INVESTING ACTIVITIES
Property, plant and equipment	(17.1)	(17.2)
Cash used in disposition of assets	(0.4)	(0.3)
Proceeds from disposition of assets	0.1	0.1
Affiliated-company property, plant and equipment transfers	0.1	0.0
Net Cash Used In Investing Activities	(17.3)	(17.4)
FINANCING ACTIVITIES
Change in notes receivable from Questar	6.1	(24.4)
Dividends paid to Questar	(48.0)	(32.0)
Net Cash Used In Financing Activities	(41.9)	(56.4)
Change in cash and cash equivalents	(6.4)	3.6
Beginning cash and cash equivalents	7.4	2.7
Ending cash and cash equivalents	$ 1.0	$ 6.3