Wexpro and Wexpro II Agreements and Stipulations (Tables)

12 Months Ended

Dec. 31, 2015

Wexpro Agreement [Abstract]

Net investment base, yearly average rate of return and oil and NGL income sharing

Wexpro's net investment base, yearly average rate of return, and oil and NGL income shared with Questar Gas are shown in the table below:

	Year Ended December 31,
	2015			2014			2013
Wexpro net investment base at December 31, (in millions)	$	642.9		$	649.0		$	589.7
Average annual rate of return (after tax)	17.5		%	17.9		%	19.7		%
Oil and NGL income sharing (in millions)	$	—		$	—		$	0.6