Stockholders' Equity (Capital Stock Activity) (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ordinary shares, shares outstanding (in shares)	449.5	447.1
Ordinary Shares Issued
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ordinary shares, shares outstanding (in shares)	449.5	447.1	450.5	465.1
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture	2.4	0.6	0.2
Treasury Stock, Shares, Retired		(4.0)	(14.8)
Ordinary Shares Held in  Employee Benefit Trust
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ordinary shares, shares outstanding (in shares)			0.1
Stock Issued During Period, Shares, New Issues		0.1	(0.1)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Shares, Acquired		4.0	14.8
Treasury Stock, Shares, Retired		(4.0)	(14.8)