CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
OPERATING ACTIVITIES
Net income	$ 78.5	$ 84.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	58.4	56.2
Deferred income taxes	(5.1)	(3.8)
Abandonment and impairment	0.2	0.0
Share-based compensation	2.7	3.2
Net (gain) from asset sales	(0.3)	0.0
(Income) from unconsolidated affiliate	(1.0)	(0.9)
Distributions from unconsolidated affiliate and other	1.5	1.5
Changes in operating assets and liabilities	198.1	82.6
NET CASH PROVIDED BY OPERATING ACTIVITIES	333.0	223.4
INVESTING ACTIVITIES
Property, plant and equipment purchased	(68.5)	(66.1)
Questar Gas acquisition of gas distribution system	0.0	(11.4)
Cash used in disposition of assets	(0.9)	(0.6)
Proceeds from disposition of assets	0.3	0.2
NET CASH USED IN INVESTING ACTIVITIES	(69.1)	(77.9)
FINANCING ACTIVITIES
Common stock issued	3.5	1.3
Common stock repurchased	(2.8)	(3.6)
Change in short-term debt	0.9	(133.0)
Long-term debt repaid	(250.0)	0.0
Capital lease obligation repaid	(0.3)	(0.3)
Revolver issuance costs paid	(1.2)	0.0
Dividends paid	(38.7)	(37.1)
Tax benefits from share-based compensation	0.1	0.0
NET CASH USED IN FINANCING ACTIVITIES	(288.5)	(172.7)
Change in cash and cash equivalents	(24.6)	(27.2)
Beginning cash and cash equivalents	25.0	32.0
Ending cash and cash equivalents	0.4	4.8
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	47.6	43.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	16.1	14.9
Deferred income taxes	1.7	(2.4)
Share-based compensation	0.4	0.3
Net (gain) from asset sales	0.0	0.0
Changes in operating assets and liabilities	125.5	80.0
NET CASH PROVIDED BY OPERATING ACTIVITIES	191.3	136.6
INVESTING ACTIVITIES
Property, plant and equipment purchased	(59.1)	(43.0)
Questar Gas acquisition of gas distribution system	0.0	(11.4)
Cash used in disposition of assets	(0.7)	(0.5)
Proceeds from disposition of assets	0.1	0.1
NET CASH USED IN INVESTING ACTIVITIES	(59.7)	(54.8)
FINANCING ACTIVITIES
Change in notes payable to Questar	(132.8)	(83.5)
Checks outstanding in excess of cash balances	0.7	0.4
Dividends paid to Questar	(10.0)	(18.5)
NET CASH USED IN FINANCING ACTIVITIES	(142.1)	(101.6)
Change in cash and cash equivalents	(10.5)	(19.8)
Beginning cash and cash equivalents	10.5	19.8
Ending cash and cash equivalents	0.0	0.0
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	14.2	13.9
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14.3	14.5
Deferred income taxes	1.2	(0.2)
Share-based compensation	0.5	0.5
Net (gain) from asset sales	(0.3)	0.0
(Income) from unconsolidated affiliate	(1.0)	(0.9)
Distributions from unconsolidated affiliate and other	1.4	1.3
Changes in operating assets and liabilities	10.5	6.2
NET CASH PROVIDED BY OPERATING ACTIVITIES	40.8	35.3
INVESTING ACTIVITIES
Property, plant and equipment purchased	(6.6)	(8.7)
Cash used in disposition of assets	(0.2)	(0.1)
Proceeds from disposition of assets	0.2	0.0
NET CASH USED IN INVESTING ACTIVITIES	(6.6)	(8.8)
FINANCING ACTIVITIES
Change in notes receivable from Questar	(27.2)	4.2
Dividends paid to Questar	(16.0)	(32.0)
NET CASH USED IN FINANCING ACTIVITIES	(43.2)	(27.8)
Change in cash and cash equivalents	(9.0)	(1.3)
Beginning cash and cash equivalents	10.2	7.4
Ending cash and cash equivalents	$ 1.2	$ 6.1