Debt (Details) (USD $)				3 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Mar. 31, 2013 Revolving credit facility [Member]	Sep. 30, 2013 Revolving credit facility [Member]	Sep. 30, 2013 Commercial paper [Member]	Dec. 31, 2012 Commercial paper [Member]	Sep. 30, 2012 Commercial paper [Member]	Sep. 30, 2013 Questar Gas [Member] 4.78% and 4.83% Notes due 2043 and 2048 [Member]	Sep. 30, 2013 Questar Gas [Member] 4.78% Notes due 2043 [Member]	Sep. 30, 2013 Questar Gas [Member] 4.83% Notes due 2048 [Member]
Short-term Debt [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity				$ 500,000,000	$ 750,000,000
Debt Instrument Maturity Dates				8/31/2016	4/19/2018
Consolidated Funded Debt Percentage Of Consolidated Capital Permitted Under Credit Arrangement Amendment					70.00%
Amounts borrowed under short-term financing arrangements	355,000,000	263,000,000	263,000,000		0	355,000,000	263,000,000	263,000,000
Questar Gas Long-term Debt Commitment [Abstract]
Debt Instrument, Face Amount									$ 150,000,000	$ 90,000,000	$ 60,000,000
Funding Date of Long-term Debt									December 2013
Long-term Debt, Life (in years)										30 years	35 years
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)										4.78%	4.83%