Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at beginning of year	$ 67.2	$ 63.8
Accretion	3.3	3.4
Liabilities incurred	6.0	3.1
Revisions in estimated cash flows	(6.9)	(1.7)
Liabilities settled	(1.9)	(1.4)
AROs at end of year	67.7	67.2
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	67.7	67.2
Questar Gas [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at end of year	0.6	0.5
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	0.6	0.5
Wexpro [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at end of year	64.9	64.6
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	64.9	64.6
Questar Pipeline [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at end of year	2.2	2.1
Asset Retirement Obligations By Line Of Business [Abstract]
AROs by line of business	$ 2.2	$ 2.1