Equity (Reconciliation of Ordinary Shares) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended					9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019
Treasury Stock, Value, Acquired, Cost Method	$ 250.1	$ 250.0	$ 14.0	$ 250.1	$ 250.0	$ 500.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of ordinary shares (shares)						0.0
Ordinary shares
Treasury Stock, Value, Acquired, Cost Method	$ 2.1	$ 2.4	$ 0.2	$ 2.8	$ 2.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (shares)	265.9	266.4	269.8	272.5	274.0	266.4
Shares issued under incentive plans, net						2.2
Repurchase of ordinary shares (shares)	(2.1)	(2.4)	(0.2)	(2.8)	(2.8)	(4.5)
Ending balance (shares)	264.1	265.5	270.1	269.8	272.5	264.1
Ordinary shares held in treasury, at cost
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (shares)		24.5				24.5
Shares issued under incentive plans, net						0.0
Ending balance (shares)	24.5					24.5