Share-based Compensation Plans (Performance Share Awards) (Details) In Millions, except Share data, unless otherwise specified	12 Months Ended											12 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2013 Ordinary Shares	Dec. 31, 2012 Ordinary Shares	Dec. 31, 2011 Ordinary Shares	Dec. 31, 2013 ADS	Dec. 31, 2012 ADS	Dec. 31, 2011 ADS	Dec. 31, 2013 EBT Ordinary Shares	Dec. 31, 2013 EBT ADS	Dec. 31, 2013 Performance Share Awards GBP (£)
Performance Share Awards Outstanding [Roll Forward]
Outstanding as at beginning of period												3,518,138
Granted												1,508,631
Exercised												(1,826,648)
Forfeited												(498,822)
Outstanding as at end of period												2,701,299
Aggregate intrinsic value (in GBP)												£ 76.9
Weighted average remaining life	5 years 6 months
Weighted average grant date fair value (in GBP per share)												£ 19.71
Tax benefit associated with exercise of stock options (in US dollar)	11.9	40.1	29.4
Intrinsic values of share-based awards exercised (in US dollar)	298.3	224.1	189.3
Cash received from employees as a result of employee share option exercises (in US dollar)	$ 17.2	$ 16.2	$ 13.4
Treasury Stock
Treasury stock held (in shares)				4,200,000	4,500,000	2,700,000	800,000	900,000	800,000	2,400,000	400,000