Condensed Consolidated Statements of Changes in Equity - USD ($) shares in Millions, $ in Millions	Total	Ordinary shares	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss
Common Stock, Dividends, Per Share, Cash Paid	$ 0.35
Beginning Balance at Dec. 31, 2017	$ 5,037.8	$ 1.8	$ 2,797.7	$ 2,481.7	$ (243.4)
Beginning Balance (in shares) at Dec. 31, 2017		180.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102.9			102.9
Other comprehensive loss, net of tax	(1.4)				(1.4)
Dividends declared, $0.18 per share	(62.6)			(62.6)
Share repurchase	(150.0)		(150.0)
Share repurchase (in shares)		(2.2)
Exercise of options, net of shares tendered for payment	5.8		5.8
Exercise of options, net of shares tendered for payment (in shares)		0.1
Issuance of restricted shares, net of cancellations (in shares)		0.3
Issuance of restricted shares, net of cancellations	0.0	$ 0.0
Shares surrendered by employees to pay taxes	(4.8)		(4.8)
Shares surrendered by employees to pay taxes (in shares)		(0.1)
Share-based compensation	6.0		6.0
Ending Balance (in shares) at Mar. 31, 2018		178.4
Ending Balance at Mar. 31, 2018	$ 4,719.7	$ 1.8	2,654.7	2,308.0	(244.8)
Common Stock, Dividends, Per Share, Cash Paid	$ 0.18
Beginning Balance at Dec. 31, 2018	$ 1,836.1	$ 1.7	1,893.8	169.2	(228.6)
Beginning Balance (in shares) at Dec. 31, 2018		171.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	51.3
Other comprehensive loss, net of tax	2.7				2.7
Dividends declared, $0.18 per share	(31.0)			(31.0)
Exercise of options, net of shares tendered for payment	9.1		9.1
Exercise of options, net of shares tendered for payment (in shares)		0.3
Issuance of restricted shares, net of cancellations (in shares)		0.2
Issuance of restricted shares, net of cancellations	0.0	$ 0.0
Shares surrendered by employees to pay taxes	(3.2)		(3.2)
Shares surrendered by employees to pay taxes (in shares)		0.0
Share-based compensation	5.4		5.4
Ending Balance (in shares) at Mar. 31, 2019		171.9
Ending Balance at Mar. 31, 2019	$ 1,870.4	$ 1.7	$ 1,905.1	$ 189.5	$ (225.9)