Rate Regulation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	$ 35.8	$ 46.7
Noncurrent regulatory assets	20.5	21.6
Current regulatory liabilities	14.1	5.8
Noncurrent regulatory liabilities	61.2	54.4
Questar Gas [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	30.2	41.0
Noncurrent regulatory assets	16.1	16.4
Current regulatory liabilities	11.1	4.3
Noncurrent regulatory liabilities	53.0	46.7
Rate Changes [Abstract]
Current authorized return on equity in Utah	10.35%
Amount of requested increase in rates in Utah	19
Requested return on equity in Utah	10.35%
Future authorized return on equity in Utah	9.85%
Amount of increase in annual revenues in Utah	7.6
Amount of increase in customer rates in Wyoming	0.6
Current authorized return on equity in Wyoming	9.16%
Questar Gas [Member] | Purchased-gas adjustment [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0	15.2
Noncurrent regulatory assets	0	0
Current regulatory liabilities	7.4	0
Noncurrent regulatory liabilities	0	0
Questar Gas [Member] | DSM [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	11.2	11.0
Noncurrent regulatory assets	0	0
Questar Gas [Member] | Deferred production taxes [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	5.7	5.0
Noncurrent regulatory assets	0	0
Regulatory asset remaining recovery period (in years)	12 months
Questar Gas [Member] | Deferred royalties [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	5.2	6.3
Noncurrent regulatory assets	0	0
Questar Gas [Member] | Contract withholding [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	8.1	3.5
Noncurrent regulatory assets	0	0
Questar Gas [Member] | Cost of reacquired debt [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0	0
Noncurrent regulatory assets	4.8	5.3
Regulatory asset remaining recovery period (in years)	9 years
Questar Gas [Member] | Pipeline integrity costs [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0	0
Noncurrent regulatory assets	9.3	8.7
Amount of allowed yearly recovery through pipeline integrity regulations	4.4
Questar Gas [Member] | ARO cost-of-service gas wells [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0	0
Noncurrent regulatory assets	2.0	2.4
Regulatory asset amortization period (in years)	18-year
Questar Gas [Member] | CET [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities	3.3	4.2
Noncurrent regulatory liabilities	0	0
Questar Gas [Member] | Cost of plant removal [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities	0	0
Noncurrent regulatory liabilities	52.7	46.2
Questar Gas [Member] | Income taxes recoverable from/refundable to customers [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities	0	0
Noncurrent regulatory liabilities	0.3	0.5
Questar Gas [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities	0.4	0.1
Noncurrent regulatory liabilities	0	0
Questar Pipeline [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	5.6	5.7
Noncurrent regulatory assets	4.4	5.2
Current regulatory liabilities	3.0	1.5
Noncurrent regulatory liabilities	8.2	7.7
Questar Pipeline [Member] | Cost of reacquired debt [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0	0
Noncurrent regulatory assets	2.6	3.0
Regulatory asset remaining recovery period (in years)	7 years
Questar Pipeline [Member] | Gas imbalance [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	5.3	4.4
Noncurrent regulatory assets	0	0
Current regulatory liabilities	3.0	1.4
Noncurrent regulatory liabilities	0	0
Questar Pipeline [Member] | Revenue sharing [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0.3	1.3
Noncurrent regulatory assets	0	0
Current regulatory liabilities	0	0.1
Noncurrent regulatory liabilities	0	0
Questar Pipeline [Member] | Income taxes recoverable from/refundable to customers [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0	0
Noncurrent regulatory assets	0.6	0.9
Questar Pipeline [Member] | Postretirement medical [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory liabilities	0	0
Noncurrent regulatory liabilities	8.2	7.7
Questar Pipeline [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Current regulatory assets	0	0
Noncurrent regulatory assets	$ 1.2	$ 1.3