Summary of Significant Accounting Policies, Textuals (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Accounting policies additional disclosures
Net non-cash LIFO (benefit) charge	$ (5.7)	$ (7.1)	$ (13.5)	$ 12.8
Excess of current cost over the stated LIFO value of inventory	15.8		15.8		29.4
Undiscounted workers' compensation liabilities	24.2		24.2		24.3
Discount rate used in estimating liabilities for worker compensation claims			0.75%		1.00%
Margin deposits with counterparties	0		0		0
Margin deposits from counterparties	$ 0		$ 0		$ 0
Performance shares
Accounting policies additional disclosures
Performance award vesting period, years			3 years
Maximum
Accounting policies additional disclosures
Number of days in maturity for commerial paper classified as cash and cash equivalents			90 days
Minimum
Accounting policies additional disclosures
Number of days in maturity for commerial paper classified as short-term investments			90 days