Accumulated Other Comprehensive Income/(Loss) (Summary of Changes in Accumulated Other Comprehensive Income/(Loss)) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 36,176.4
Other comprehensive loss before reclassifications	(679.2)	$ 2,476.0
Amounts reclassified from AOCI	(69.4)	(9.3)
Net current period other comprehensive loss	(748.6)	2,466.7
Ending balance	37,290.2
Accumulated other comprehensive income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,375.0	(1,497.6)
Net current period other comprehensive loss	(748.6)
Ending balance	626.4	969.1
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,279.6	(1,505.4)
Other comprehensive loss before reclassifications	(679.2)	2,441.1
Amounts reclassified from AOCI	0.0	0.0
Net current period other comprehensive loss	(679.2)	2,441.1
Ending balance	600.4	935.7
Pension and other employee benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	27.5	(5.2)
Other comprehensive loss before reclassifications	0.0	9.7
Amounts reclassified from AOCI	(1.5)	1.3
Net current period other comprehensive loss	(1.5)	11.0
Ending balance	26.0	5.8
Unrealized holding gain/(loss) on available-for-sale debt securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	67.9	6.6
Other comprehensive loss before reclassifications	0.0	24.7
Amounts reclassified from AOCI	(67.9)	(4.4)
Net current period other comprehensive loss	(67.9)	20.3
Ending balance	$ 0.0	26.9
Hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		6.4
Other comprehensive loss before reclassifications		0.5
Amounts reclassified from AOCI		(6.2)
Net current period other comprehensive loss		(5.7)
Ending balance		$ 0.7