Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, par value (per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	342,857,143	342,857,143
Common stock, shares issued (in shares)	143,300,449	142,677,449
Common stock, shares outstanding (in shares)	115,865,510	118,897,295
Treasury stock, shares at cost (in shares)	27,434,939	23,780,154
Series C Preferred Stock
Preferred stock, shares outstanding (in shares)	0	5,200,000
Series D Preferred Stock
Preferred stock, shares authorized (in shares)	100,000,000	0
Preferred stock, shares issued (in shares)	8,000,000	0
Preferred stock, shares outstanding (in shares)	8,000,000	0