Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 13, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	QUESTAR GAS CO
Entity Central Index Key	0000068589
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		9,189,626