GOODWILL (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Beginning balance	[1]	$ 5.6	$ 5.6
No events affecting goodwill		0.0	0.0
Ending balance	[1]	5.6	5.6
Operating Segments | Questar Gas
Goodwill [Roll Forward]
Beginning balance	[1]	5.6	5.6
No events affecting goodwill		0.0	0.0
Ending balance	[1]	5.6	5.6
Operating Segments | Corporate and Other
Goodwill [Roll Forward]
Beginning balance	[1]	0.0	0.0
No events affecting goodwill		0.0	0.0
Ending balance	[1]	$ 0.0	$ 0.0

[1] There are no accumulated impairment losses.