CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Net income	$ 39.4	$ 39.2	$ 112.3	$ 114.4	$ 209.9	$ 212.1
Other comprehensive income (loss):
Pension and other postretirement benefits	7.9	6.6	15.7	13.2	(30.5)	(153.7)
Interest rate cash flow hedges	0.1	0.1	0.3	0.2	0.5	(37.8)
Change in fair value of long-term investment	(0.1)	0	(0.1)	0	0	0
Income taxes	(3.0)	(2.5)	(6.0)	(5.1)	11.4	72.9
Net other comprehensive income (loss)	4.9	4.2	9.9	8.3	(18.6)	(118.6)
COMPREHENSIVE INCOME	44.3	43.4	122.2	122.7	191.3	93.5
Questar Pipeline [Member]
Net income	14.5	16.1	30.3	32.7	62.3	68.7
Other comprehensive income (loss):
Interest rate cash flow hedges	0.1	0.1	0.3	0.2	0.5	(37.8)
Income taxes	0	0	(0.1)	(0.1)	(0.2)	14.0
Net other comprehensive income (loss)	0.1	0.1	0.2	0.1	0.3	(23.8)
COMPREHENSIVE INCOME	$ 14.6	$ 16.2	$ 30.5	$ 32.8	$ 62.6	$ 44.9