CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	342,857,143	342,857,143
Common stock, shares issued (in shares)	143,077,973	142,677,449
Common stock, shares outstanding (in shares)	117,841,369	118,897,295
Treasury stock, shares at cost (in shares)	25,236,604	23,780,154
Series D Preferred Stock
Preferred Stock, shares authorized (in shares)	100,000,000
Preferred Stock, shares issued (in shares)	8,000,000
Preferred stock, shares outstanding (in shares)	8,000,000
Series C Preferred Stock
Preferred Stock, shares issued (in shares)	5,200,000	5,200,000
Preferred stock, shares outstanding (in shares)	5,200,000	5,200,000