Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2015	Dec. 31, 2014
Stockholders' Equity Attributable to Parent [Abstract]
Common stock, par value (in usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized	1,200,000,000	1,200,000,000
Common stock, shares issued	673,501,593	673,501,593
Treasury stock, common shares	173,777,130	159,202,872