Accumulated Other Comprehensive Income/(Loss) (Summary of Changes in Accumulated Other Comprehensive Income/(Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 28,948.0	$ 9,829.1	$ 8,662.9
Other comprehensive income/(loss) before reclassifications	2,893.0
Amounts reclassified from AOCI	(20.4)	(47.0)
Net current period other comprehensive income/(loss)	2,872.6	(1,313.8)	(152.3)
Ending balance	36,176.4	28,948.0	9,829.1
Accumulated other comprehensive (loss)/income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,497.6)	(183.8)	(31.5)
Other comprehensive income/(loss) before reclassifications		(1,266.8)
Amounts reclassified from AOCI		(47.0)
Net current period other comprehensive income/(loss)	2,872.6	(1,313.8)	(152.3)
Ending balance	1,375.0	(1,497.6)	(183.8)
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,505.4)	(182.1)
Other comprehensive income/(loss) before reclassifications	2,785.0	(1,323.3)
Amounts reclassified from AOCI	0.0	0.0
Net current period other comprehensive income/(loss)	2,785.0	(1,323.3)
Ending balance	1,279.6	(1,505.4)	(182.1)
Pension and other employee benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5.2)	0.0
Other comprehensive income/(loss) before reclassifications	33.4	38.3
Amounts reclassified from AOCI	(0.7)	(43.5)
Net current period other comprehensive income/(loss)	32.7	(5.2)
Ending balance	27.5	(5.2)	0.0
Unrealized holding gain/(loss) on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6.6	(1.7)
Other comprehensive income/(loss) before reclassifications	75.2	8.3
Amounts reclassified from AOCI	(13.9)	0.0
Net current period other comprehensive income/(loss)	61.3	8.3
Ending balance	67.9	6.6	(1.7)
Hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6.4	0.0
Other comprehensive income/(loss) before reclassifications	(0.6)	9.9
Amounts reclassified from AOCI	(5.8)	(3.5)
Net current period other comprehensive income/(loss)	(6.4)	6.4
Ending balance	$ 0.0	$ 6.4	$ 0.0