Rate Regulation (Tables)

12 Months Ended

Dec. 31, 2015

Regulated Operations [Abstract]

Details of regulatory assets and liabilities

The following table details regulatory assets and liabilities:

	December 31, 2015				December 31, 2014
	Current		Noncurrent		Current		Noncurrent
	(in millions)
Regulatory assets:
Questar Gas
Purchased-gas adjustment	$	18.9	$	—	$	39.2	$	—
Energy-efficiency program	1.1		—		—		—
Contract withholding	20.3		—		13.6		—
Deferred cost-of-service gas charges	19.5		8.1		25.5		9.3
Cost of reacquired debt	—		3.8		—		4.3
Pipeline integrity costs	6.3		—		—		7.7
Conservation Enabling Tariff	3.6		—		—		—
Other	0.1		—		—		—
Total Questar Gas regulatory assets	69.8		11.9		78.3		21.3
Questar Pipeline
Gas imbalance	—		—		1.2		—
Revenue sharing	0.2		—		0.1		—
Cost of reacquired debt	—		1.8		—		2.2
Income taxes recoverable from customers	—		—		—		0.3
Other	—		1.2		—		1.2
Total Questar Pipeline regulatory assets	0.2		3.0		1.3		3.7
Total regulatory assets	$	70.0	$	14.9	$	79.6	$	25.0
Regulatory liabilities:
Questar Gas
Energy-efficiency program	—		—		0.3		—
Conservation Enabling Tariff	—		—		12.1		—
Cost of plant removal	3.7		65.5		—		60.7
Income taxes refundable to customers	—		0.1		—		0.2
Other	0.3		—		0.1		—
Total Questar Gas regulatory liabilities	4.0		65.6		12.5		60.9
Questar Pipeline
Gas imbalance	2.3		—		0.8		—
Revenue sharing	0.1		—		0.1		—
Postretirement medical	—		10.0		—		9.0
Total Questar Pipeline regulatory liabilities	2.4		10.0		0.9		9.0
Total regulatory liabilities	$	6.4	$	75.6	$	13.4	$	69.9