CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 212.0	$ 207.9	$ 340.5
Other comprehensive income (loss)
Change in unrecognized actuarial loss	(35.7)	(162.9)	17.7
Change in unrecognized prior-service costs	2.7	3.0	3.8
Interest rate cash flow hedges	0.4	(37.2)	0
Change in fair value of long-term investment	0.1	0	0.1
Discontinued operations
Change in unrealized fair value of derivatives held by QEP	0	0	(138.7)
Income taxes	12.3	75.0	43.4
Net other comprehensive income (loss)	(20.2)	(122.1)	(73.7)
COMPREHENSIVE INCOME	191.8	85.8	266.8
Discontinued operations, noncontrolling interest	0	0	(1.3)
COMPREHENSIVE INCOME ATTRIBUTABLE TO QUESTAR	191.8	85.8	265.5
Questar Pipeline [Member]
Net income	64.7	67.9	67.4
Other comprehensive income (loss)
Interest rate cash flow hedges	0.4	(37.2)	0
Discontinued operations
Income taxes	(0.2)	13.8	0
Net other comprehensive income (loss)	0.2	(23.4)	0
COMPREHENSIVE INCOME	$ 64.9	$ 44.5	$ 67.4