Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock, par value (US$ per share)	$ 100	$ 100
Common stock, par value (US$ per share)	$ 0.01	$ 0.01
Common stock, authorized shares	600,000,000	600,000,000
Common stock, issued shares	174,500,000	220,500,000
Common stock, outstanding shares	174,300,000	219,800,000