Consolidated Balance Sheets (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
2.822% convertible perpetual preferred stock, par value (in dollars)	$ 0.01	$ 0.01
2.822% convertible perpetual preferred stock, shares issued	0	250,000
2.822% convertible perpetual preferred stock, shares outstanding	0	250,000
Common stock, par value (in dollars)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	417,583,825	416,939,950
Common stock, shares outstanding	315,443,011	314,190,042
Treasury stock, shares	102,140,814	102,749,908
Convertible Preferred Stock [Member]
Preferred Stock, Dividend Rate Amended, Percentage	2.822%	2.822%