CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Current Assets
Cash and cash equivalents	$ 0	$ 16,800,000	$ 0
Accounts receivable, net	58,000,000	114,300,000	60,000,000
Unbilled gas accounts receivable	11,700,000	78,300,000	10,600,000
Gas stored underground	59,400,000	39,000,000	62,100,000
Materials and supplies	24,000,000	24,500,000	25,700,000
Current regulatory assets	49,300,000	46,700,000	56,800,000
Prepaid expenses and other	6,000,000	13,100,000	6,500,000
Deferred income taxes - current	8,800,000	13,000,000	6,500,000
Total Current Assets	217,200,000	345,700,000	228,200,000
Property, Plant and Equipment	5,583,800,000	5,333,300,000	5,244,400,000
Accumulated depreciation, depletion and amortization	(2,088,800,000)	(2,016,300,000)	(1,983,200,000)
Net Property, Plant and Equipment	3,495,000,000	3,317,000,000	3,261,200,000
Investment in unconsolidated affiliate	25,800,000	26,500,000	26,800,000
Noncurrent regulatory assets	21,300,000	21,600,000	21,700,000
Other noncurrent assets	50,900,000	46,300,000	44,500,000
TOTAL ASSETS	3,810,200,000	3,757,100,000	3,582,400,000
Current Liabilities
Checks outstanding in excess of cash balances	1,600,000	0	5,400,000
Short-term debt	355,000,000	263,000,000	263,000,000
Accounts payable and accrued expenses	211,600,000	235,200,000	215,600,000
Current regulatory liabilities	1,800,000	5,800,000	4,300,000
Current portion of long-term debt and capital lease obligation	800,000	42,700,000	109,200,000
Total Current Liabilities	570,800,000	546,700,000	597,500,000
Long-term debt and capital lease obligation, less current portion	1,136,100,000	1,138,200,000	988,900,000
Deferred income taxes	645,900,000	603,400,000	563,500,000
Asset retirement obligations	65,900,000	67,200,000	66,300,000
Defined benefit pension plan and other postretirement benefits	257,300,000	303,700,000	246,900,000
Customer contributions in aid of construction	31,500,000	22,900,000	30,400,000
Regulatory and other noncurrent liabilities	44,100,000	39,400,000	39,300,000
COMMON SHAREHOLDERS' EQUITY
Common stock	449,700,000	442,400,000	457,800,000
Retained earnings	839,600,000	839,500,000	805,500,000
Accumulated other comprehensive (loss)	(230,700,000)	(246,300,000)	(213,700,000)
Total Common Shareholders' Equity	1,058,600,000	1,035,600,000	1,049,600,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	3,810,200,000	3,757,100,000	3,582,400,000
Questar Gas [Member]
Current Assets
Cash and cash equivalents	0	1,400,000	0
Accounts receivable, net	24,200,000	67,000,000	26,900,000
Unbilled gas accounts receivable	11,700,000	78,200,000	10,500,000
Accounts receivable from affiliates	31,400,000	31,800,000	22,200,000
Gas stored underground	56,500,000	38,300,000	58,400,000
Materials and supplies	12,200,000	13,500,000	13,500,000
Current regulatory assets	45,500,000	41,000,000	52,400,000
Prepaid expenses and other	2,400,000	3,200,000	2,800,000
Deferred income taxes - current	1,500,000	1,500,000	0
Total Current Assets	185,400,000	275,900,000	186,700,000
Property, Plant and Equipment	2,147,800,000	2,040,900,000	2,013,600,000
Accumulated depreciation, depletion and amortization	(790,300,000)	(762,800,000)	(758,600,000)
Net Property, Plant and Equipment	1,357,500,000	1,278,100,000	1,255,000,000
Noncurrent regulatory assets	16,500,000	16,400,000	16,000,000
Goodwill	5,600,000	5,600,000	5,600,000
Other noncurrent assets	3,000,000	3,100,000	2,100,000
TOTAL ASSETS	1,568,000,000	1,579,100,000	1,465,400,000
Current Liabilities
Checks outstanding in excess of cash balances	1,400,000	0	2,000,000
Notes payable to Questar	195,000,000	166,100,000	206,600,000
Accounts payable and accrued expenses	80,300,000	105,000,000	72,800,000
Accounts payable to affiliates	49,900,000	50,900,000	46,200,000
Customer advances	21,900,000	30,200,000	32,200,000
Current regulatory liabilities	500,000	4,300,000	1,800,000
Deferred income taxes - current	0	0	4,000,000
Current portion of long-term debt and capital lease obligation	0	42,000,000	108,500,000
Total Current Liabilities	349,000,000	398,500,000	474,100,000
Long-term debt and capital lease obligation, less current portion	384,500,000	384,500,000	234,500,000
Deferred income taxes	330,700,000	301,600,000	270,800,000
Customer contributions in aid of construction	31,500,000	22,900,000	30,400,000
Regulatory and other noncurrent liabilities	3,400,000	4,000,000	3,800,000
COMMON SHAREHOLDERS' EQUITY
Common stock	23,000,000	23,000,000	23,000,000
Additional paid-in capital	173,600,000	172,500,000	172,200,000
Retained earnings	272,300,000	272,100,000	256,600,000
Total Common Shareholders' Equity	468,900,000	467,600,000	451,800,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	1,568,000,000	1,579,100,000	1,465,400,000
Questar Pipeline [Member]
Current Assets
Cash and cash equivalents	1,500,000	7,100,000	400,000
Notes receivable from Questar	36,600,000	38,700,000	42,000,000
Accounts receivable, net	17,800,000	19,100,000	19,800,000
Accounts receivable from affiliates	32,700,000	27,500,000	28,200,000
Gas stored underground	2,900,000	700,000	3,700,000
Materials and supplies	7,500,000	6,500,000	7,000,000
Current regulatory assets	3,800,000	5,700,000	4,400,000
Prepaid expenses and other	1,800,000	7,700,000	1,900,000
Deferred income taxes - current	1,600,000	1,600,000	1,800,000
Total Current Assets	106,200,000	114,600,000	109,200,000
Property, Plant and Equipment	1,766,100,000	1,840,100,000	1,821,900,000
Accumulated depreciation, depletion and amortization	(617,800,000)	(629,300,000)	(618,700,000)
Net Property, Plant and Equipment	1,148,300,000	1,210,800,000	1,203,200,000
Investment in unconsolidated affiliate	25,800,000	26,500,000	26,800,000
Goodwill	4,200,000	4,200,000	4,200,000
Regulatory and other noncurrent assets	8,200,000	9,000,000	9,500,000
TOTAL ASSETS	1,292,700,000	1,365,100,000	1,352,900,000
Current Liabilities
Accounts payable and accrued expenses	35,900,000	25,700,000	66,500,000
Accounts payable to affiliates	3,700,000	16,900,000	3,200,000
Current regulatory liabilities	1,300,000	1,500,000	2,500,000
Total Current Liabilities	40,900,000	44,100,000	72,200,000
Long-term debt and capital lease obligation, less current portion	458,800,000	458,900,000	458,900,000
Deferred income taxes	226,900,000	242,500,000	201,800,000
Regulatory and other noncurrent liabilities	13,900,000	13,800,000	13,800,000
COMMON SHAREHOLDERS' EQUITY
Common stock	6,600,000	6,600,000	6,600,000
Additional paid-in capital	349,200,000	347,500,000	347,100,000
Retained earnings	219,300,000	274,900,000	275,700,000
Accumulated other comprehensive (loss)	(22,900,000)	(23,200,000)	(23,200,000)
Total Common Shareholders' Equity	552,200,000	605,800,000	606,200,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	$ 1,292,700,000	$ 1,365,100,000	$ 1,352,900,000