Condensed Balance Sheets Parenthetical (USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
ASSETS
Accumulated depreciation	$ 1,287.3	$ 1,259.1	$ 1,191.2
Shareholders' equity:
Common stock, par value	$ 1.00	$ 1.00	$ 1.00
Common stock, authorized	120.0	120.0	120.0
Common stock, issued	79.0	79.4	80.3
Common stock, outstanding	79.0	79.4	80.3