Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	$ (183.8)
Net current period other comprehensive income/(loss)	24.4
As at March 31,	(159.4)
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	(182.1)	$ (25.7)
Net current period other comprehensive income/(loss)	24.7	(129.5)
As at March 31,	(157.4)	(155.2)
Unrealized holding gain/(loss) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	(1.7)	(5.8)
Net current period other comprehensive income/(loss)	(0.3)	0.7
As at March 31,	(2.0)	(5.1)
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	(183.8)	(31.5)
Net current period other comprehensive income/(loss)	24.4	(128.8)
As at March 31,	$ (159.4)	$ (160.3)