Consolidated Balance Sheets (Parenthetical) - $ / shares |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Statement of Financial Position [Abstract] | ||
| Common stock, par value | $ 5 | $ 5 |
| Common stock, authorized shares | 325,000,000 | 325,000,000 |
| Common stock, issued shares | 228,164,824 | 228,164,824 |
| Shares in treasury | 55,690,402 | 55,306,483 |