CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING ACTIVITIES
Net income	$ 207.9	$ 340.5	$ 395.9
Discontinued operations, net of income taxes	0	(148.2)	(215.4)
Adjustments to reconcile net income to net cash provided by operating activities of continuing operations:
Depreciation, depletion and amortization	169.4	161.8	154.3
Deferred income taxes	96.2	91.4	82.1
Share-based compensation	10.1	15.4	9.3
Net (gain) from asset sales	(0.2)	(0.4)	(0.2)
(Income) from unconsolidated affiliate	(3.8)	(3.8)	(3.8)
Distributions from unconsolidated affiliate	4.4	4.0	3.3
Other operating	0.1	(1.5)	0
Changes in operating assets and liabilities
Accounts receivable	7.7	2.9	21.7
Inventories	(3.3)	0.1	24.1
Prepaid expenses	(2.1)	0	(0.2)
Accounts payable and accrued expenses	11.7	(18.4)	(16.9)
Interest rate hedge - current liability	(37.3)	0	0
Federal income taxes	37.1	(33.8)	10.2
Regulatory assets and liabilities	31.2	(34.8)	(38.2)
Other	(40.1)	(24.3)	2.6
Net Cash Provided By Operating Activities Of Continuing Operations	489.0	350.9	428.8
INVESTING ACTIVITIES
Property, plant and equipment	(367.7)	(320.3)	(299.8)
Equity investment in QEP	0	(250.0)	0
Cash used in disposition of assets	(3.5)	(2.6)	(2.0)
Proceeds from disposition of assets and other	0.3	0.6	1.9
Change in notes receivable	0	39.3	50.1
Distribution from QEP	0	7.3	0
Net Cash Used In Investing Activities Of Continuing Operations	(370.9)	(525.7)	(249.8)
FINANCING ACTIVITIES
Common stock issued	7.6	17.9	16.3
Common stock repurchased	(4.9)	(11.1)	(7.2)
Long-term debt issued, net of issuance costs	174.9	244.6	50.8
Long-term debt repaid	(182.0)	0	(42.0)
Change in long-term note payable	0	0	(50.0)
Change in short-term debt	(23.0)	73.0	(62.1)
Change in notes payable	0	(52.9)	12.2
Checks outstanding in excess of cash balances	0	0	(1.2)
Dividends paid	(110.1)	(94.8)	(87.9)
Tax benefits from share-based compensation	9.2	8.4	3.6
Net Cash Provided By (Used in) Financing Activities Of Continuing Operations	(128.3)	185.1	(167.5)
CASH PROVIDED BY (USED IN) CONTINUING OPERATIONS	(10.2)	10.3	11.5
Cash provided by operating activities of discontinued operations	0	475.5	1,149.4
Cash used in investing activities of discontinued operations	0	(598.6)	(1,146.4)
Cash provided by (used in) financing activities of discontinued operations	0	103.8	(8.8)
Effect of change in cash and cash equivalents of discontinued operations	0	19.3	5.8
Change in cash and cash equivalents	(10.2)	10.3	11.5
Beginning cash and cash equivalents	21.8	11.5	0
Ending cash and cash equivalents	11.6	21.8	11.5
Supplemental Disclosure of Cash Paid (Received) During the Year for:
Interest	54.2	55.4	59.0
Income taxes	(21.0)	44.6	6.4
Questar Pipeline [Member]
OPERATING ACTIVITIES
Net income	67.9	67.4	58.2
Adjustments to reconcile net income to net cash provided by operating activities of continuing operations:
Depreciation and amortization	53.9	49.9	47.1
Deferred income taxes	34.5	17.2	26.3
Share-based compensation	1.8	1.3	1.1
Net (gain) from asset sales	(0.3)	(0.8)	(0.5)
(Income) from unconsolidated affiliate	(3.8)	(3.8)	(3.8)
Distributions from unconsolidated affiliate	4.4	4.0	3.3
Other operating	0.1	(1.5)	0
Changes in operating assets and liabilities
Accounts receivable	(0.8)	(2.0)	4.4
Inventories	(0.2)	(1.2)	0.2
Prepaid expenses	0	(0.3)	(0.9)
Accounts payable and accrued expenses	0.8	8.5	(10.4)
Interest rate hedge - current liability	(37.3)	0	0
Federal income taxes	1.1	0.6	(4.5)
Regulatory assets and liabilities	(5.0)	1.0	2.4
Net Cash Provided By Operating Activities Of Continuing Operations	117.1	140.3	122.9
INVESTING ACTIVITIES
Property, plant and equipment	(104.5)	(121.0)	(100.8)
Cash used in disposition of assets	(1.3)	(1.1)	(0.4)
Proceeds from disposition of assets and other	0.1	0.1	1.6
Affiliated-company property, plant and equipment transfers	(0.1)	0	(0.1)
Net Cash Used In Investing Activities Of Continuing Operations	(105.8)	(122.0)	(99.7)
FINANCING ACTIVITIES
Long-term debt issued, net of issuance costs	176.2	0	50.8
Long-term debt repaid	(180.0)	0	(42.0)
Change in notes receivable from Questar	21.5	12.4	(2.1)
Change in notes payable to Questar	0	(0.2)	0
Dividends paid	(30.9)	(29.0)	(27.9)
Net Cash Provided By (Used in) Financing Activities Of Continuing Operations	(13.2)	(16.8)	(21.2)
Change in cash and cash equivalents	(1.9)	1.5	2.0
Beginning cash and cash equivalents	5.3	3.8	1.8
Ending cash and cash equivalents	3.4	5.3	3.8
Supplemental Disclosure of Cash Paid (Received) During the Year for:
Interest	24.7	29.0	29.3
Income taxes	1.6	19.2	12.4
Questar Gas [Member]
OPERATING ACTIVITIES
Net income	46.1	43.9	41.6
Adjustments to reconcile net income to net cash provided by operating activities of continuing operations:
Depreciation and amortization	49.2	48.0	47.8
Deferred income taxes	25.2	43.6	34.1
Share-based compensation	1.1	1.4	1.0
Changes in operating assets and liabilities
Accounts receivable	5.0	(4.4)	7.7
Inventories	(1.3)	3.4	21.2
Prepaid expenses	(0.2)	0.5	(1.4)
Accounts payable and accrued expenses	(1.8)	(21.6)	0.8
Federal income taxes	6.2	(8.5)	7.9
Regulatory assets and liabilities	17.4	(37.0)	(41.4)
Net Cash Provided By Operating Activities Of Continuing Operations	146.9	69.3	119.3
INVESTING ACTIVITIES
Property, plant and equipment	(121.5)	(108.6)	(82.6)
Cash used in disposition of assets	(2.2)	(1.5)	(1.6)
Proceeds from disposition of assets and other	0.2	0.5	0.3
Affiliated-company property, plant and equipment transfers	0.1	0	0.1
Net Cash Used In Investing Activities Of Continuing Operations	(123.4)	(109.6)	(83.8)
FINANCING ACTIVITIES
Equity contribution	20.0	0	0
Long-term debt repaid	(2.0)	0	0
Change in notes payable to Questar	(10.9)	66.6	(1.3)
Dividends paid	(30.3)	(28.8)	(28.2)
Net Cash Provided By (Used in) Financing Activities Of Continuing Operations	(23.2)	37.8	(29.5)
Change in cash and cash equivalents	0.3	(2.5)	6.0
Beginning cash and cash equivalents	4.7	7.2	1.2
Ending cash and cash equivalents	5.0	4.7	7.2
Supplemental Disclosure of Cash Paid (Received) During the Year for:
Interest	25.1	25.5	27.9
Income taxes	$ (3.9)	$ (9.7)	$ (18.4)