Share Capital (Movements in Treasury Shares) (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Beginning balance	92.4	95.9	81.3
Acquisition of common shares	16.0	1.9	19.6
Distribution of common shares	(5.2)	(5.2)	(4.7)
Common shares distributed to meet ESPP obligation	(0.2)	(0.2)	(0.3)
Ending balance	103.0	92.4	95.9