CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$ 226.5	$ 161.2	$ 212.0
Pension and other postretirement benefits
Change in unrecognized actuarial loss	(97.5)	167.7	(35.7)
Change in unrecognized prior service cost	0.6	1.1	2.7
Interest rate cash flow hedge amortization	0.5	0.5	0.4
Change in fair value of long-term investment	0	(0.1)	0.1
Income taxes	36.9	(64.7)	12.3
Net other comprehensive income (loss)	(59.5)	104.5	(20.2)
COMPREHENSIVE INCOME	167.0	265.7	191.8
Questar Pipeline [Member]
Net income	60.6	8.2	64.7
Pension and other postretirement benefits
Interest rate cash flow hedge amortization	0.5	0.5	0.4
Income taxes	(0.1)	(0.2)	(0.2)
Net other comprehensive income (loss)	0.4	0.3	0.2
COMPREHENSIVE INCOME	$ 61.0	$ 8.5	$ 64.9