Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares authorized	100,000	100,000
Preferred stock, par value per share	$ 100	$ 100
Common stock, shares authorized	500,000,000	500,000,000
Common stock, par value per share	$ 1.00	$ 1.00
Common stock, shares issued	256,992,261	256,537,535
Number of treasury shares held	102,168,868	101,109,186
Share Repurchases [Line Items]
Number of shares authorized to be repurchased	20,000,000
Payments for Repurchase of Common Stock	$ 105,023	$ 0	$ 600,164
January 2015 Authorization [Member]
Share Repurchases [Line Items]
Number of shares authorized to be repurchased	15,000,000
Payments for Repurchase of Common Stock			$ 600,164
Shares repurchased	1,059,682		8,228,542
Average price per share for repurchased shares (in dollars per share)	$ 99.11		$ 72.94
Remaining number of shares authorized to be repurchased	5,711,776