CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) Parenthetical (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Plan and Restoration of Retirement Income Plan:
Amortization of deferred net loss	$ 0.8	$ 0.5	$ 1.2	$ 0.9
Amortization of prior service cost	0.1	0.1	0.1	0.1
Postretirement Benefit Plans:
Amortization of deferred net loss	0.3	0.3	0.6	0.6
Amortization of prior service cost	(0.2)	(0.2)	(0.5)	(0.5)
Deferred commodity contracts hedging gains reclassified in net income	0	0	(0.1)	(1.7)
Deferred commodity contracts hedging losses	0	(0.2)	0	(0.2)
Amortization of deferred interest rate swap hedging losses	$ 0	$ 0	$ 0.1	$ 0.1