CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
CONSOLIDATED BALANCE SHEETS
Property, plant and equipment; accumulated depreciation, depletion and amortization (in dollars)	$ 2,534.4	$ 2,447.5
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	72,101,077	71,935,838
Treasury stock, shares	6,515,251	6,515,251