CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Net income	$ 85.1	$ 72.9	$ 173.4	$ 209.7
Other comprehensive income (loss):
Pension and other postretirement benefits	4.3	7.8	165.3	(31.8)
Interest rate cash flow hedges	0.2	0.2	0.5	0.5
Change in fair value of long-term investment	0	0	(0.1)	0.1
Income taxes	(1.8)	(3.0)	(63.5)	11.9
Net other comprehensive income (loss)	2.7	5.0	102.2	(19.3)
COMPREHENSIVE INCOME	87.8	77.9	275.6	190.4
Questar Pipeline [Member]
Net income	15.7	15.8	8.1	63.9
Other comprehensive income (loss):
Interest rate cash flow hedges	0.2	0.2	0.5	0.5
Income taxes	(0.1)	(0.1)	(0.2)	(0.2)
Net other comprehensive income (loss)	0.1	0.1	0.3	0.3
COMPREHENSIVE INCOME	$ 15.8	$ 15.9	$ 8.4	$ 64.2