Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	$ (31.5)
Net current period other comprehensive (loss)/income	(123.6)
As at September 30,	(155.1)
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	(25.7)	$ 110.4
Other comprehensive (loss)/ income before reclassification		(75.9)
Gain transferred to the income statement (within Other income),net) on disposal of available-for-sale-securities		0.0
Net current period other comprehensive (loss)/income	(124.9)	(75.9)
As at September 30,	(150.6)	34.5
Unrealized holding gain/(loss) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	(5.8)	(0.2)
Other comprehensive (loss)/ income before reclassification		5.6
Gain transferred to the income statement (within Other income),net) on disposal of available-for-sale-securities		(9.1)
Net current period other comprehensive (loss)/income	1.3	(3.5)
As at September 30,	(4.5)	(3.7)
Accumulated other comprehensive (loss)/income
Accumulated Other Comprehensive Income (Loss) [Line Items]
As at January 1,	(31.5)	110.2
Other comprehensive (loss)/ income before reclassification		(70.3)
Gain transferred to the income statement (within Other income),net) on disposal of available-for-sale-securities		(9.1)
Net current period other comprehensive (loss)/income	(123.6)	(79.4)
As at September 30,	$ (155.1)	$ 30.8