CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011
Net income	$ 75.2	$ 69.9	$ 213.2	$ 259.5
Other comprehensive income (loss):
Pension and other postretirement benefits	0	0	(159.9)	21.5
Interest rate cash flow hedges	0.1	0	(37.1)	0
Change in unrealized fair value of derivatives - discontinued operations	0	0	0	(437.9)
Income taxes	(0.1)	0	74.9	154.7
Net other comprehensive income (loss)	0	0	(122.1)	(261.7)
COMPREHENSIVE INCOME (LOSS)	75.2	69.9	91.1	(2.2)
Discontinued operations, noncontrolling interest	0	0	0	(0.7)
COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO QUESTAR	75.2	69.9	91.1	(2.9)
Questar Pipeline [Member]
Net income	16.6	15.3	69.2	65.5
Other comprehensive income (loss):
Interest rate cash flow hedges	0.1	0	(37.1)	0
Income taxes	(0.1)	0	13.7	0
Net other comprehensive income (loss)	0	0	(23.4)	0
COMPREHENSIVE INCOME (LOSS)	$ 16.6	$ 15.3	$ 45.8	$ 65.5