CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Current Assets
Cash and cash equivalents	$ 0	$ 11.6	$ 0
Accounts receivable, net	60.0	123.9	74.8
Unbilled gas accounts receivable	10.6	75.4	12.6
Gas stored underground	62.1	40.3	49.6
Materials and supplies	25.7	25.7	24.4
Current regulatory assets	56.8	31.7	38.3
Prepaid expenses and other	6.5	10.7	6.1
Deferred income taxes - current	6.5	16.1	14.4
Total Current Assets	228.2	335.4	220.2
Property, plant and equipment	5,244.4	4,984.1	4,869.4
Accumulated depreciation, depletion and amortization	(1,983.2)	(1,885.7)	(1,858.4)
Net property, plant and equipment	3,261.2	3,098.4	3,011.0
Investment in unconsolidated affiliate	26.8	27.3	27.6
Noncurrent regulatory assets	21.7	21.0	21.9
Other noncurrent assets	44.5	50.7	47.7
TOTAL ASSETS	3,582.4	3,532.8	3,328.4
Current Liabilities
Checks outstanding in excess of cash balances	5.4	0	9.6
Short-term debt	263.0	219.0	278.0
Accounts payable and accrued expenses	215.6	242.9	206.8
Current regulatory liabilities	4.3	15.4	3.2
Current portion of long-term debt and capital lease obligation	109.2	91.5	25.0
Total Current Liabilities	597.5	568.8	522.6
Long-term debt and capital lease obligation, less current portion	988.9	993.0	881.4
Deferred income taxes	555.9	500.2	548.5
Asset retirement obligations	66.3	63.8	64.5
Defined benefit pension plan and other postretirement benefits	266.7	309.7	148.2
Customer contributions-in-aid-of-construction	30.4	26.6	33.8
Regulatory and other noncurrent liabilities	39.3	37.2	35.4
COMMON SHAREHOLDERS' EQUITY
Common stock	457.8	514.7	508.6
Retained earnings	805.5	744.9	712.2
Accumulated other comprehensive (loss)	(225.9)	(226.1)	(126.8)
Total Common Shareholders' Equity	1,037.4	1,033.5	1,094.0
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	3,582.4	3,532.8	3,328.4
Questar Gas [Member]
Current Assets
Cash and cash equivalents	0	5.0	0
Accounts receivable, net	26.9	77.6	24.1
Unbilled gas accounts receivable	10.5	75.2	12.3
Accounts receivable from affiliates	22.2	1.8	2.4
Gas stored underground	58.4	40.3	49.6
Materials and supplies	13.5	12.2	12.2
Current regulatory assets	52.4	26.5	38.2
Prepaid expenses and other	2.8	3.1	2.5
Deferred income taxes - current	0	5.6	3.9
Total Current Assets	186.7	247.3	145.2
Property, plant and equipment	2,013.6	1,927.0	1,879.3
Accumulated depreciation, depletion and amortization	(758.6)	(749.6)	(742.2)
Net property, plant and equipment	1,255.0	1,177.4	1,137.1
Noncurrent regulatory assets	16.0	15.1	15.5
Goodwill	5.6	5.6	5.6
Other noncurrent assets	2.1	2.3	2.4
TOTAL ASSETS	1,465.4	1,447.7	1,305.8
Current Liabilities
Checks outstanding in excess of cash balances	2.0	0	3.2
Notes payable to Questar	206.6	142.7	97.9
Accounts payable and accrued expenses	72.8	112.3	63.6
Accounts payable to affiliates	46.2	41.9	38.6
Customer advances	32.2	25.0	23.8
Current regulatory liabilities	1.8	14.2	1.3
Deferred income taxes - current	4.0	0	0
Current portion of long-term debt and capital lease obligation	108.5	91.5	25.0
Total Current Liabilities	474.1	427.6	253.4
Long-term debt and capital lease obligation, less current portion	234.5	276.5	343.0
Deferred income taxes	270.8	259.8	250.9
Customer contributions-in-aid-of-construction	30.4	26.6	33.8
Regulatory and other noncurrent liabilities	3.8	4.8	5.2
COMMON SHAREHOLDERS' EQUITY
Common stock	23.0	23.0	23.0
Additional paid-in capital	172.2	171.4	151.1
Retained earnings	256.6	258.0	245.4
Total Common Shareholders' Equity	451.8	452.4	419.5
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	1,465.4	1,447.7	1,305.8
Questar Pipeline [Member]
Current Assets
Cash and cash equivalents	0.4	3.4	0.4
Notes receivable from Questar	42.0	8.8	0
Accounts receivable, net	19.8	19.1	18.8
Accounts receivable from affiliates	28.2	20.2	19.8
Gas stored underground	3.7	0	0
Materials and supplies	7.0	7.4	7.2
Current regulatory assets	4.4	5.2	0.1
Prepaid expenses and other	1.9	4.4	1.9
Deferred income taxes - current	1.8	1.8	1.1
Total Current Assets	109.2	70.3	49.3
Property, plant and equipment	1,821.9	1,790.4	1,780.1
Accumulated depreciation, depletion and amortization	(618.7)	(586.7)	(579.5)
Net property, plant and equipment	1,203.2	1,203.7	1,200.6
Investment in unconsolidated affiliate	26.8	27.3	27.6
Goodwill	4.2	4.2	4.2
Regulatory and other noncurrent assets	9.5	10.1	9.0
TOTAL ASSETS	1,352.9	1,315.6	1,290.7
Current Liabilities
Notes payable to Questar	0	0	130.3
Accounts payable and accrued expenses	66.5	31.7	70.0
Accounts payable to affiliates	3.2	5.5	3.0
Current regulatory liabilities	2.5	1.2	1.9
Total Current Liabilities	72.2	38.4	205.2
Long-term debt and capital lease obligation, less current portion	458.9	459.0	280.9
Deferred income taxes	201.8	201.4	195.9
Regulatory and other noncurrent liabilities	13.8	14.7	15.9
COMMON SHAREHOLDERS' EQUITY
Common stock	6.6	6.6	6.6
Additional paid-in capital	347.1	345.7	345.3
Retained earnings	275.7	273.2	263.7
Accumulated other comprehensive (loss)	(23.2)	(23.4)	(22.8)
Total Common Shareholders' Equity	606.2	602.1	592.8
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	$ 1,352.9	$ 1,315.6	$ 1,290.7