Accumulated Other Comprehensive Loss (Summary of Changes in Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	$ (1,497.6)
Other comprehensive income (loss) before reclassifications	274.7
Amounts reclassified from AOCL	(4.2)
Net current period other comprehensive income / (loss)	270.5
As of March 31,	(1,227.1)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	(1,497.6)	$ (183.8)
Net current period other comprehensive income / (loss)	270.5	24.4
As of March 31,	(1,227.1)	(159.4)
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	(1,505.4)	(182.1)
Other comprehensive income (loss) before reclassifications	265.5
Amounts reclassified from AOCL	0.0
Net current period other comprehensive income / (loss)	265.5	24.7
As of March 31,	(1,239.9)	(157.4)
Pension and other employee benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	(5.2)	0.0
Other comprehensive income (loss) before reclassifications	7.4
Amounts reclassified from AOCL	0.0
Net current period other comprehensive income / (loss)	7.4	0.0
As of March 31,	2.2	0.0
Unrealized holding gain on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	6.6	(1.7)
Other comprehensive income (loss) before reclassifications	2.1
Amounts reclassified from AOCL	0.0
Net current period other comprehensive income / (loss)	2.1	(0.3)
As of March 31,	8.7	(2.0)
Hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
As at January 1,	6.4	0.0
Other comprehensive income (loss) before reclassifications	(0.3)
Amounts reclassified from AOCL	(4.2)
Net current period other comprehensive income / (loss)	(4.5)	0.0
As of March 31,	$ 1.9	$ 0.0