CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
OPERATING ACTIVITIES
Net income	$ 84.6	$ 85.1
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	56.2	57.2
Deferred income taxes	(3.8)	(1.2)
Share-based compensation	3.2	3.2
(Income) from unconsolidated affiliate	(0.9)	(0.9)
Distributions from unconsolidated affiliate and other	1.5	1.6
Changes in operating assets and liabilities	82.6	67.9
Net Cash Provided By Operating Activities	223.4	212.9
INVESTING ACTIVITIES
Property, plant and equipment	(66.1)	(69.7)
Questar Gas acquisition of gas distribution system	(11.4)	0
Cash used in disposition of assets	(0.6)	(0.9)
Proceeds from disposition of assets	0.2	0
Net Cash Used In Investing Activities	(77.9)	(70.6)
FINANCING ACTIVITIES
Common stock issued	1.3	0.5
Common stock repurchased	(3.6)	(2.8)
Change in short-term debt	(133.0)	(119.0)
Capital lease obligation repaid	0.3	0.3
Dividends paid	(37.1)	(31.6)
Tax benefits from share-based compensation	0	0.5
Net Cash Provided By (Used In) Financing Activities	(172.7)	(152.7)
Change in cash and cash equivalents	(27.2)	(10.4)
Beginning cash and cash equivalents	32.0	16.0
Ending cash and cash equivalents	4.8	5.6
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	43.8	39.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.9	14.6
Deferred income taxes	(2.4)	(0.1)
Share-based compensation	0.3	0.3
Changes in operating assets and liabilities	80.0	45.3
Net Cash Provided By Operating Activities	136.6	99.7
INVESTING ACTIVITIES
Property, plant and equipment	(43.0)	(48.9)
Questar Gas acquisition of gas distribution system	(11.4)	0
Cash used in disposition of assets	(0.5)	(0.9)
Proceeds from disposition of assets	0.1	0
Net Cash Used In Investing Activities	(54.8)	(49.8)
FINANCING ACTIVITIES
Change in notes receivable from Questar	0	(30.6)
Change in notes payable to Questar	(83.5)	(17.7)
Checks outstanding in excess of cash balances	0.4	0
Dividends paid to Questar	(18.5)	(9.0)
Net Cash Provided By (Used In) Financing Activities	(101.6)	(57.3)
Change in cash and cash equivalents	(19.8)	(7.4)
Beginning cash and cash equivalents	19.8	8.8
Ending cash and cash equivalents	0	1.4
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	13.9	15.7
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.5	14.1
Deferred income taxes	(0.2)	(0.1)
Share-based compensation	0.5	0.6
(Income) from unconsolidated affiliate	(0.9)	(0.9)
Distributions from unconsolidated affiliate and other	1.3	1.5
Changes in operating assets and liabilities	6.2	13.0
Net Cash Provided By Operating Activities	35.3	43.9
INVESTING ACTIVITIES
Property, plant and equipment	(8.7)	(8.5)
Cash used in disposition of assets	(0.1)	0
Net Cash Used In Investing Activities	(8.8)	(8.5)
FINANCING ACTIVITIES
Change in notes receivable from Questar	4.2	(17.2)
Dividends paid to Questar	(32.0)	(16.0)
Net Cash Provided By (Used In) Financing Activities	(27.8)	(33.2)
Change in cash and cash equivalents	(1.3)	2.2
Beginning cash and cash equivalents	7.4	2.7
Ending cash and cash equivalents	$ 6.1	$ 4.9