CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net income	$ 39.2	$ 40.3	$ 114.4	$ 110.2	$ 212.1	$ 201.6
Other comprehensive income (loss):
Pension and other postretirement benefits	0	0	0	0	(159.9)	(4.0)
Interest rate cash flow hedges	0.1	0.8	0.2	0.8	(37.8)	0.8
Income taxes	0	(0.3)	(0.1)	(0.3)	75.2	1.1
Net other comprehensive income (loss)	0.1	0.5	0.1	0.5	(122.5)	(2.1)
COMPREHENSIVE INCOME	39.3	40.8	114.5	110.7	89.6	199.5
Questar Pipeline [Member]
Net income	16.1	16.6	32.7	31.9	68.7	66.2
Other comprehensive income (loss):
Interest rate cash flow hedges	0.1	0.8	0.2	0.8	(37.8)	0.8
Income taxes	0	(0.3)	(0.1)	(0.3)	14.0	(0.3)
Net other comprehensive income (loss)	0.1	0.5	0.1	0.5	(23.8)	0.5
COMPREHENSIVE INCOME	$ 16.2	$ 17.1	$ 32.8	$ 32.4	$ 44.9	$ 66.7