CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
CONSOLIDATED BALANCE SHEETS
Property, plant and equipment, accumulated depreciation, depletion and amortization (in dollars)	$ 2,899.7	$ 2,757.1
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	59,305,690	62,961,628
Treasury stock, shares	1,274,837	10,940