Consolidated Balance Sheets (Parenthetical) - £ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common Stock, Par Value (in GBP per share)	£ 0.05	£ 0.05
Common Stock, Shares Authorized	1,500,000,000	1,500,000,000
Common Stock, Shares, Issued	917,100,000	912,200,000
Common Stock, Shares, Outstanding	917,100,000	912,200,000
Treasury Stock, Shares	8,400,000	9,100,000