Share-Based Compensation Stock options (Detail) - Stock Options [Member] $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) installments $ / shares shares	Dec. 31, 2014 shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Stock option minimum term (in years)	5 years
Stock option maximum term (in years)	10 years
Stock option majority minimum term (in years)	7 years
Stock option majority maximum term (in years)	10 years
Minimum number of installments for vesting of options held by employees | installments	3
Maximum number of installments for vesting of options held by employees | installments	4
Number of unvested options at end of period | shares	0	0
Stock option transactions under the terms of the LTSIP - shares [Roll Forward]
Balance at December 31, 2014 | shares	435,507
Granted | shares	0
Exercised | shares	(178,112)
Forfeited | shares	0
Balance at December 31, 2015 | shares	257,395
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at December 31, 2014	$ 12.46
Exercised	11.47
Balance at December 31, 2015	$ 13.14
Stock options, additional disclosures [Abstract]
Aggregate intrinsic value of outstanding options (in shares) | $	$ 1.6
Aggregate intrinsic value of exercisable options | $	$ 1.6
Number of Questar stock options held by certain officers, employees and nonemployee directors of QEP (in shares) | shares	64,093
Weighted-average exercise price of Questar stock options awarded to certain officers, employees and nonemployee directors of QEP (in dollars per share)	$ 12.16
Weighted-average remaining life of Questar stock options held by certain officers, employees and nonemployee directors of QEP (in years)	7 months
Options Outstanding Exercise Price Range 1 [Member]
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Minimum exercise price of options outstanding (in dollars per share)	$ 11.40
Maximum exercise price of options outstanding (in dollars per share)	$ 17.35
Number of outstanding options at end of period (in shares) | shares	257,395
Weighted-average remaining term (in years and months)	10 months
Weighted-average exercise price (in dollars per share)	$ 13.14
Number of exercisable options at end of period (in shares) | shares	257,395
Weighted-average exercise price, options exercisable (in dollars per share)	$ 13.14
Minimum [Member]
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at December 31, 2014	11.40
Exercised	11.40
Balance at December 31, 2015	11.40
Maximum [Member]
Stock option transactions under the terms of the LTSIP - exercise price [Roll Forward]
Balance at December 31, 2014	17.35
Exercised	13.10
Balance at December 31, 2015	$ 17.35
Questar Gas [Member]
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Number of outstanding options at end of period (in shares) | shares	0
Questar Pipeline [Member]
Stock options outstanding, exercisable and unvested at end of period, by exercise price range [Abstract]
Minimum exercise price of options outstanding (in dollars per share)	$ 11.40
Maximum exercise price of options outstanding (in dollars per share)	$ 13.10
Number of outstanding options at end of period (in shares) | shares	47,995
Weighted-average remaining term (in years and months)	6 months
Weighted-average exercise price (in dollars per share)	$ 11.98
Number of exercisable options at end of period (in shares) | shares	47,995
Weighted-average exercise price, options exercisable (in dollars per share)	$ 11.98