Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2013	$ 86.9
Other comprehensive income, net of tax	23.3	26.6	(25.4)
As at December 31, 2013	110.2	86.9
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2013	85.1
Other Comprehensive income before reclassification	25.3
Gain transferred to the income statement (within Other (expense)/income,net) on disposal of available-for-sale-securities	0
Other comprehensive income, net of tax	25.3
As at December 31, 2013	110.4
Unrealized holding gain/(loss) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2013	1.8
Other Comprehensive income before reclassification	1.5
Gain transferred to the income statement (within Other (expense)/income,net) on disposal of available-for-sale-securities	(3.5)
Other comprehensive income, net of tax	(2.0)
As at December 31, 2013	(0.2)
Accumulated other comprehensive income
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2013	86.9
Other Comprehensive income before reclassification	26.8
Gain transferred to the income statement (within Other (expense)/income,net) on disposal of available-for-sale-securities	(3.5)
Other comprehensive income, net of tax	23.3	26.6	(25.4)
As at December 31, 2013	$ 110.2	$ 86.9