Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	$ (183.8)
Net current period other comprehensive income/(loss)	(202.0)
As at June 30,	(385.8)
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)	(195.5)	(83.3)
As at June 30,	(377.6)	(109.0)
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)	(4.7)	3.3
As at June 30,	(6.4)	(2.5)
Hedging activities
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	0.0
Net current period other comprehensive income/(loss)	(1.8)	0.0
As at June 30,	(1.8)	0.0
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)	(202.0)	(80.0)
As at June 30,	$ (385.8)	$ (111.5)