CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net income	$ 40.3	$ 39.4	$ 125.4	$ 112.3	$ 174.3	$ 209.9
Other comprehensive income (loss):
Pension and other postretirement benefits	4.5	7.9	8.8	15.7	161.9	(30.5)
Interest rate cash flow hedge amortization	0.1	0.1	0.3	0.3	0.5	0.5
Change in fair value of long-term investment	0	(0.1)	0	(0.1)	0	0
Income taxes	(1.8)	(3.0)	(3.6)	(6.0)	(62.3)	11.4
Net other comprehensive income (loss)	2.8	4.9	5.5	9.9	100.1	(18.6)
COMPREHENSIVE INCOME	43.1	44.3	130.9	122.2	274.4	191.3
Questar Pipeline [Member]
Net income	15.7	14.5	31.4	30.3	9.3	62.3
Other comprehensive income (loss):
Interest rate cash flow hedge amortization	0.1	0.1	0.3	0.3	0.5	0.5
Income taxes	0	0	(0.1)	(0.1)	(0.2)	(0.2)
Net other comprehensive income (loss)	0.1	0.1	0.2	0.2	0.3	0.3
COMPREHENSIVE INCOME	$ 15.8	$ 14.6	$ 31.6	$ 30.5	$ 9.6	$ 62.6