Goodwill (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Goodwill [Line Items]
Goodwill arising on business acquired	$ 1,837.0	$ 1,773.8
Goodwill [Roll Forward]
As at January 1,	2,474.9	624.6
Acquisition	1,837.0	1,773.8
Foreign currency translation	(22.3)	(24.7)
As at September 30,	$ 4,289.6	$ 2,373.7