Condensed Balance Sheets Parenthetical (USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
ASSETS
Accumulated depreciation	$ 1,168.8	$ 1,144.0	$ 1,089.8
Shareholders' equity:
Common stock, par value	$ 1.00	$ 1.00	$ 1.00
Common stock, authorized	120.0	120.0	120.0
Common stock, issued	80.1	80.1	79.7
Common stock, outstanding	80.1	80.1	79.7