Common and Preferred Stock (Details) - $ / shares shares in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Common: Par value $.25, 600,000,000 shares authorized
Treasury stock	52.9		39.9
Common Stock, par value and shares authorized
Common stock, par value per share	$ 0.25	$ 0.25
Common stock shares authorized	600.0	600.0