Debt (Tables)

12 Months Ended

Dec. 31, 2015

Debt Disclosure [Abstract]

Schedule of Short-term Debt

The details of short-term debt are as follows:

	December 31,
	2015			2014
	(in millions)
Commercial paper with various interest rates	$	457.6		$	347.0
Weighted-average interest rate at end of year	0.50		%	0.23		%

Schedule of Notes Payable

The following table details the notes payable to Questar from Questar Gas and the associated interest rates. There were no notes payable to Questar from Questar Pipeline at December 31, 2015 or 2014.

	December 31,
	2015			2014
	(in millions)
Questar Gas
Notes payable to Questar	$	273.3		$	119.3
Interest rate at end of year	0.35		%	0.25		%

Schedule of Debt

The details of long-term debt are as follows:

	December 31,
	2015			2014
	(in millions)
Questar Corporation
2.75% Notes due 2016	$	250.0		$	250.0
Questar Gas
5.31% and 6.85% Medium-term Notes due 2017 and 2018	84.5			84.5
6.30% Notes due 2018	50.0			50.0
2.98% Notes due 2024	40.0			40.0
3.28% Notes due 2027	110.0			110.0
7.20% Notes due 2038	100.0			100.0
4.78% Notes due 2043	90.0			90.0
4.83% Notes due 2048	60.0			60.0
Total Questar Gas long-term debt	534.5			534.5
Questar Pipeline
6.48% Medium-term Notes due 2018	5.0			30.1
5.83% Notes due 2018	250.0			250.0
4.875% Notes due 2041	180.0			180.0
Total Questar Pipeline long-term debt	435.0			460.1
Total long-term debt outstanding	1,219.5			1,244.6
Less current portion	(250.2		)	(25.1		)
Less unamortized debt discount	(1.7		)	(1.9		)
Plus unamortized debt premium	0.3			0.5
Plus fair value hedge adjustment	0.2			2.0
Total long-term debt, less current portion	$	968.1		$	1,220.1

Schedule of Debt Maturities

The aggregate maturities of Questar Corporation, Questar Gas and Questar Pipeline long-term debt for the next five years are as follows:

	Questar Corporation		Questar Gas		Questar Pipeline		Total
	Years Ending December 31,
	(in millions)
2016	$	250.0	$	—	$	—	$	250.0
2017	—		14.5		—		14.5
2018	—		120.0		255.0		375.0
2019	—		—		—		—
2020	—		—		—		—