CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES
Net income	$ 208.7	$ 226.5	$ 161.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	223.5	234.4	201.8
Deferred income taxes	59.5	49.2	42.4
Abandonment and impairment	12.5	2.0	80.6
Share-based compensation	11.4	12.4	10.2
Net (gain) loss from asset sales	(1.8)	(1.2)	0.2
(Income) from unconsolidated affiliate	(3.7)	(3.5)	(3.7)
Distributions from unconsolidated affiliate	4.5	4.4	4.6
Other operating	1.1	0.9	0.9
Changes in operating assets and liabilities
Accounts receivable, including unbilled gas sales	(11.4)	29.5	(41.5)
Inventories	0.6	(10.4)	(0.2)
Prepaid expenses and other	(1.1)	(1.7)	3.6
Accounts payable, accrued expenses and other	(15.1)	(19.6)	33.7
Federal income taxes	(32.8)	(24.0)	6.2
Current regulatory assets and liabilities	2.6	(44.5)	19.2
Noncurrent regulatory and other assets and liabilities	(47.1)	(10.8)	(17.1)
NET CASH PROVIDED BY OPERATING ACTIVITIES	411.4	443.6	502.1
INVESTING ACTIVITIES
Property, plant and equipment	(306.8)	(319.1)	(399.4)
Wexpro acquisition of producing properties	(12.2)	(52.4)	(104.3)
Questar Gas acquisition	(11.4)	0.0	0.0
Cash used in disposition of assets	(6.2)	(4.8)	(4.9)
Proceeds from disposition of assets	1.1	9.5	0.6
NET CASH USED IN INVESTING ACTIVITIES	(335.5)	(366.8)	(508.0)
FINANCING ACTIVITIES
Common stock issued	3.5	2.9	2.3
Common stock repurchased	(23.3)	(4.1)	(4.2)
Long-term debt issued, net of issuance costs	0.0	0.0	147.3
Long-term debt repaid	(25.1)	0.0	(42.0)
Capital lease obligation repaid	(1.2)	(0.9)	(0.7)
Change in short-term debt	110.6	71.0	13.0
Dividends paid	(148.0)	(131.9)	(124.6)
Tax benefits from share-based compensation	0.6	2.2	14.0
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	(82.9)	(60.8)	5.1
Change in cash and cash equivalents	(7.0)	16.0	(0.8)
Beginning cash and cash equivalents	32.0	16.0	16.8
Ending cash and cash equivalents	25.0	32.0	16.0
Supplemental Disclosure of Cash Paid (Received) During the Year for:
Interest	62.0	61.3	55.8
Income taxes	89.0	97.4	33.6
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	64.3	55.2	52.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	60.6	58.8	54.7
Deferred income taxes	52.9	46.0	37.7
Share-based compensation	1.4	1.6	1.4
Net (gain) loss from asset sales	0.0	(0.1)	0.0
Changes in operating assets and liabilities
Accounts receivable, including unbilled gas sales	(32.7)	4.6	(43.7)
Inventories	(1.5)	(8.2)	0.5
Prepaid expenses and other	0.0	(0.5)	0.2
Accounts payable, accrued expenses and other	12.7	(0.2)	29.5
Federal income taxes	(40.6)	9.2	(2.8)
Current regulatory assets and liabilities	0.0	(46.7)	17.6
Noncurrent regulatory and other assets and liabilities	(1.0)	(6.0)	5.4
NET CASH PROVIDED BY OPERATING ACTIVITIES	116.1	113.7	153.3
INVESTING ACTIVITIES
Property, plant and equipment	(217.4)	(174.7)	(166.2)
Questar Gas acquisition	(11.4)	0.0	0.0
Cash used in disposition of assets	(3.9)	(3.4)	(3.9)
Proceeds from disposition of assets	0.4	0.8	0.3
Affiliated-company property, plant and equipment transfers	(0.1)	0.0	10.8
NET CASH USED IN INVESTING ACTIVITIES	(232.4)	(177.3)	(159.0)
FINANCING ACTIVITIES
Long-term debt issued, net of issuance costs	0.0	0.0	149.0
Long-term debt repaid	0.0	0.0	(42.0)
Change in notes payable to Questar	154.0	101.6	(58.4)
Dividends paid	(47.0)	(27.0)	(35.5)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	107.0	74.6	13.1
Change in cash and cash equivalents	(9.3)	11.0	7.4
Beginning cash and cash equivalents	19.8	8.8	1.4
Ending cash and cash equivalents	10.5	19.8	8.8
Supplemental Disclosure of Cash Paid (Received) During the Year for:
Interest	27.6	26.3	21.0
Income taxes	21.1	(13.2)	(13.8)
Supplemental Disclosure of Noncash Investing and Financing Transaction:
Noncash reduction in notes payable to Questar due to equity contribution			90.0
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	59.6	60.6	8.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	57.1	56.9	58.1
Deferred income taxes	10.1	12.6	(14.3)
Abandonment and impairment	0.0	0.0	80.6
Share-based compensation	2.0	2.1	2.0
Net (gain) loss from asset sales	(0.2)	0.5	0.0
(Income) from unconsolidated affiliate	(3.7)	(3.5)	(3.7)
Distributions from unconsolidated affiliate	4.5	4.4	4.6
Other operating	0.6	0.5	0.5
Changes in operating assets and liabilities
Accounts receivable, including unbilled gas sales	(14.6)	(1.3)	(8.5)
Inventories	2.4	(2.2)	(0.9)
Prepaid expenses and other	(0.1)	0.1	3.3
Accounts payable, accrued expenses and other	3.0	(7.6)	0.4
Federal income taxes	(7.7)	(3.6)	2.9
Current regulatory assets and liabilities	3.3	4.5	2.1
NET CASH PROVIDED BY OPERATING ACTIVITIES	116.3	124.0	135.3
INVESTING ACTIVITIES
Property, plant and equipment	(40.6)	(59.4)	(73.4)
Cash used in disposition of assets	(2.3)	(1.4)	(1.0)
Proceeds from disposition of assets	0.3	0.2	0.1
Affiliated-company property, plant and equipment transfers	0.1	0.0	(10.7)
NET CASH USED IN INVESTING ACTIVITIES	(42.5)	(60.6)	(85.0)
FINANCING ACTIVITIES
Long-term debt repaid	(25.1)	0.0	0.0
Change in notes receivable from Questar	34.1	(10.7)	9.3
Dividends paid	(80.0)	(48.0)	(64.0)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	(71.0)	(58.7)	(54.7)
Change in cash and cash equivalents	2.8	4.7	(4.4)
Beginning cash and cash equivalents	7.4	2.7	7.1
Ending cash and cash equivalents	10.2	7.4	2.7
Supplemental Disclosure of Cash Paid (Received) During the Year for:
Interest	25.0	25.4	25.2
Income taxes	$ 24.8	$ 32.4	$ 11.0