STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$ 292.6	$ 280.3	$ 263.3
Other comprehensive income (loss), net of tax
Deferred commodity contracts hedging (gains) losses reclassified in net income, net of tax of $0.8, $0.7 and ($0.1), respectively	1.3	1.2	(0.4)
Comprehensive income (loss)	293.9	281.5	262.9
Retained Earnings [Member]
Net income	$ 292.6	$ 280.3	$ 263.3