Condensed Balance Sheets Parenthetical - USD ($) shares in Millions, $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
ASSETS
Accumulated depreciation	$ 1,411.9	$ 1,330.7	$ 1,324.6
Shareholders' equity:
Common stock, par value	$ 1.00	$ 1.00	$ 1.00
Common stock, authorized	120.0	120.0	120.0
Common stock, issued	77.6	77.4	78.2
Common stock, outstanding	77.6	77.4	78.2