Accumulated Other Comprehensive Loss (Summary of Changes in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	$ (183.8)
Net current period other comprehensive income	49.6
As at September 30,	(134.2)
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	(182.1)	$ (25.7)
Net current period other comprehensive income	38.8	(124.9)
As at September 30,	(143.3)	(150.6)
Unrealized holding (loss)/gain on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	(1.7)	(5.8)
Net current period other comprehensive income	10.4	1.3
As at September 30,	8.7	(4.5)
Hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	0.0	0.0
Net current period other comprehensive income	0.4	0.0
As at September 30,	0.4	0.0
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	(183.8)	(31.5)
Net current period other comprehensive income	49.6	(123.6)
As at September 30,	$ (134.2)	$ (155.1)