CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Current Assets
Cash and cash equivalents	$ 0	$ 16,800,000	$ 0
Accounts receivable, net	86,500,000	114,300,000	73,100,000
Unbilled gas accounts receivable	12,400,000	78,300,000	12,400,000
Gas stored underground	19,500,000	39,000,000	29,800,000
Materials and supplies	26,000,000	24,500,000	29,500,000
Current regulatory assets	36,000,000	46,700,000	25,200,000
Prepaid expenses and other	9,800,000	13,100,000	9,700,000
Deferred income taxes - current	17,200,000	13,000,000	16,200,000
Total Current Assets	207,400,000	345,700,000	195,900,000
Property, Plant and Equipment	5,492,700,000	5,333,300,000	5,170,100,000
Accumulated depreciation, depletion and amortization	(2,089,000,000)	(2,016,300,000)	(1,959,300,000)
Net Property, Plant and Equipment	3,403,700,000	3,317,000,000	3,210,800,000
Investment in unconsolidated affiliate	25,900,000	26,500,000	27,100,000
Noncurrent regulatory assets	20,400,000	21,600,000	20,100,000
Other noncurrent assets	49,500,000	46,300,000	43,500,000
TOTAL ASSETS	3,706,900,000	3,757,100,000	3,497,400,000
Current Liabilities
Checks outstanding in excess of cash balances	500,000	0	11,800,000
Short-term debt	206,000,000	263,000,000	190,000,000
Accounts payable and accrued expenses	186,500,000	235,200,000	164,500,000
Current regulatory liabilities	8,000,000	5,800,000	5,100,000
Current portion of long-term debt and capital lease obligation	2,800,000	42,700,000	132,200,000
Total Current Liabilities	403,800,000	546,700,000	503,600,000
Long-term debt and capital lease obligation, less current portion	1,136,900,000	1,138,200,000	991,600,000
Deferred income taxes	667,400,000	603,400,000	566,000,000
Asset retirement obligations	62,400,000	67,200,000	65,600,000
Defined benefit pension plan and other postretirement benefits	264,900,000	303,700,000	253,000,000
Customer contributions in aid of construction	26,900,000	22,900,000	28,100,000
Regulatory and other noncurrent liabilities	42,900,000	39,400,000	37,500,000
COMMON SHAREHOLDERS' EQUITY
Common stock	447,700,000	442,400,000	468,300,000
Retained earnings	890,400,000	839,500,000	801,500,000
Accumulated other comprehensive (loss)	(236,400,000)	(246,300,000)	(217,800,000)
Total Common Shareholders' Equity	1,101,700,000	1,035,600,000	1,052,000,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	3,706,900,000	3,757,100,000	3,497,400,000
Questar Gas [Member]
Current Assets
Cash and cash equivalents	0	1,400,000	0
Accounts receivable, net	49,500,000	67,000,000	28,400,000
Unbilled gas accounts receivable	12,400,000	78,200,000	12,300,000
Accounts receivable from affiliates	31,900,000	31,800,000	22,700,000
Gas stored underground	19,100,000	38,300,000	29,400,000
Materials and supplies	13,700,000	13,500,000	12,900,000
Current regulatory assets	31,000,000	41,000,000	18,500,000
Prepaid expenses and other	4,400,000	3,200,000	4,000,000
Deferred income taxes - current	5,700,000	1,500,000	5,600,000
Total Current Assets	167,700,000	275,900,000	133,800,000
Property, Plant and Equipment	2,097,800,000	2,040,900,000	1,990,700,000
Accumulated depreciation, depletion and amortization	(777,300,000)	(762,800,000)	(763,800,000)
Net Property, Plant and Equipment	1,320,500,000	1,278,100,000	1,226,900,000
Noncurrent regulatory assets	16,100,000	16,400,000	15,100,000
Goodwill	5,600,000	5,600,000	5,600,000
Other noncurrent assets	3,000,000	3,100,000	2,100,000
TOTAL ASSETS	1,512,900,000	1,579,100,000	1,383,500,000
Current Liabilities
Checks outstanding in excess of cash balances	3,400,000	0	5,400,000
Notes payable to Questar	137,300,000	166,100,000	102,100,000
Accounts payable and accrued expenses	73,700,000	105,000,000	78,800,000
Accounts payable to affiliates	55,100,000	50,900,000	43,600,000
Customer advances	9,000,000	30,200,000	19,900,000
Current regulatory liabilities	7,100,000	4,300,000	3,400,000
Current portion of long-term debt and capital lease obligation	2,000,000	42,000,000	131,500,000
Total Current Liabilities	287,600,000	398,500,000	384,700,000
Long-term debt and capital lease obligation, less current portion	384,500,000	384,500,000	236,500,000
Deferred income taxes	323,600,000	301,600,000	260,600,000
Customer contributions in aid of construction	26,900,000	22,900,000	28,100,000
Regulatory and other noncurrent liabilities	3,900,000	4,000,000	4,500,000
COMMON SHAREHOLDERS' EQUITY
Common stock	23,000,000	23,000,000	23,000,000
Additional paid-in capital	173,200,000	172,500,000	172,000,000
Retained earnings	290,200,000	272,100,000	274,100,000
Total Common Shareholders' Equity	486,400,000	467,600,000	469,100,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	1,512,900,000	1,579,100,000	1,383,500,000
Questar Pipeline [Member]
Current Assets
Cash and cash equivalents	5,700,000	7,100,000	300,000
Notes receivable from Questar	34,400,000	38,700,000	18,800,000
Accounts receivable, net	18,600,000	19,100,000	18,900,000
Accounts receivable from affiliates	32,600,000	27,500,000	27,900,000
Materials and supplies	8,200,000	7,200,000	9,000,000
Current regulatory assets	5,000,000	5,700,000	6,700,000
Prepaid expenses and other	3,800,000	7,700,000	3,700,000
Deferred income taxes - current	1,600,000	1,600,000	1,800,000
Total Current Assets	109,900,000	114,600,000	87,100,000
Property, Plant and Equipment	1,868,600,000	1,840,100,000	1,804,600,000
Accumulated depreciation, depletion and amortization	(651,100,000)	(629,300,000)	(609,200,000)
Net Property, Plant and Equipment	1,217,500,000	1,210,800,000	1,195,400,000
Investment in unconsolidated affiliate	25,900,000	26,500,000	27,100,000
Goodwill	4,200,000	4,200,000	4,200,000
Regulatory and other noncurrent assets	7,800,000	9,000,000	8,900,000
TOTAL ASSETS	1,365,300,000	1,365,100,000	1,322,700,000
Current Liabilities
Accounts payable and accrued expenses	32,400,000	25,700,000	40,000,000
Accounts payable to affiliates	5,000,000	16,900,000	4,000,000
Current regulatory liabilities	900,000	1,500,000	1,700,000
Total Current Liabilities	38,300,000	44,100,000	45,700,000
Long-term debt and capital lease obligation, less current portion	458,900,000	458,900,000	459,000,000
Deferred income taxes	248,500,000	242,500,000	200,200,000
Regulatory and other noncurrent liabilities	14,300,000	13,800,000	13,500,000
COMMON SHAREHOLDERS' EQUITY
Common stock	6,600,000	6,600,000	6,600,000
Additional paid-in capital	348,500,000	347,500,000	346,600,000
Retained earnings	273,200,000	274,900,000	274,400,000
Accumulated other comprehensive (loss)	(23,000,000)	(23,200,000)	(23,300,000)
Total Common Shareholders' Equity	605,300,000	605,800,000	604,300,000
TOTAL LIABILITIES AND COMMON SHAREHOLDERS' EQUITY	$ 1,365,300,000	$ 1,365,100,000	$ 1,322,700,000