CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME Parenthetical (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plan and Restoration of Retirement Income Plan:
Amortization of deferred net loss	$ 1.7	$ 1.4	$ 1.2
Net gain (loss) arising during the period	(5.6)	(6.7)	4.4
Amortization of prior service cost	0.2	0.2	0.1
Postretirement plans:
Amortization of deferred net loss	(1.1)	(1.6)	0.6
Net loss arising during the period	(1.1)	(3.1)	(2.4)
Amortization of deferred net transition obligation	0.1	0.1	0.1
Amortization of prior service cost	(1.0)	(1.6)	0.1
Prior service credit arising during the period	0	9.5	0
Deferred commodity contracts hedging (gains) losses reclassified in net income	(1.6)	12.6	9.9
Deferred commodity contracts hedging gains (losses)	0.1	(1.7)	(8.5)
Amortization of deferred interest rate swap hedging losses	$ 0.2	$ 0.2	$ 0.2