Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Current Assets:
Allowances, accounts and notes receivable	$ 10.4	$ 9.6
Accumulated depreciation	$ 907.7	$ 880.6
Stockholders' deficit:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	87,170,197	87,170,197
Treasury stock, shares	50,006,069	48,820,969