Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2014	$ 110.2
Other comprehensive income, net of tax	13.9
As at June 30, 2014	124.1
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2014	110.4
Other Comprehensive income before reclassification	10.2
Gain transferred to the income statement (within Other income/(expense),net) on disposal of available-for-sale-securities	0
Other comprehensive income, net of tax	10.2
As at June 30, 2014	120.6
Unrealized holding gain/(loss) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2014	(0.2)
Other Comprehensive income before reclassification	6.9
Gain transferred to the income statement (within Other income/(expense),net) on disposal of available-for-sale-securities	(3.2)
Other comprehensive income, net of tax	3.7
As at June 30, 2014	3.5
Accumulated other comprehensive income
Accumulated Other Comprehensive Income (Loss)
As at January 1, 2014	110.2
Other Comprehensive income before reclassification	17.1
Gain transferred to the income statement (within Other income/(expense),net) on disposal of available-for-sale-securities	(3.2)
Other comprehensive income, net of tax	13.9
As at June 30, 2014	$ 124.1