Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Stockholders' equity:
Common stock, shares authorized	500,000,000	500,000,000	500,000,000
Common stock, par value	$ 1.00	$ 1.00	$ 1.00
Common stock, shares issued	195,843,297	195,843,297	195,843,297
Treasury shares	538,921	538,921	538,921