STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 280.3	$ 263.3	$ 215.7
Other comprehensive income (loss), net of tax
Deferred commodity contracts hedging losses reclassified in net income, net of tax of $0.9, $0.6 and $0.3, respectively	1.5	0.9	0.5
Deferred commodity contracts hedging losses, net of tax of ($0.2), ($0.7) and ($1.4), respectively	(0.3)	(1.3)	(2.2)
Other comprehensive income (loss), net of tax	1.2	(0.4)	(1.7)
Comprehensive income (loss)	$ 281.5	$ 262.9	$ 214.0