Accumulated Other Comprehensive Income/(Loss) (Summary of Changes in Accumulated Other Comprehensive Income/(Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 36,176.4
Other comprehensive income before reclassifications	539.5	$ 274.7
Amounts reclassified from AOCI	(68.4)	(4.2)
Net current period other comprehensive income/(loss)	471.1	270.5
Ending balance	37,400.0
Accumulated other comprehensive income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,375.0	(1,497.6)
Amounts reclassified from AOCI	0.5	(4.2)
Net current period other comprehensive income/(loss)	471.1
Ending balance	1,846.1	(1,227.1)
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,279.6	(1,505.4)
Other comprehensive income before reclassifications	539.5	265.5
Amounts reclassified from AOCI	0.0	0.0
Net current period other comprehensive income/(loss)	539.5	265.5
Ending balance	1,819.1	(1,239.9)
Pension and other employee benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	27.5	(5.2)
Other comprehensive income before reclassifications	0.0	7.4
Amounts reclassified from AOCI	(0.5)	0.0
Net current period other comprehensive income/(loss)	(0.5)	7.4
Ending balance	27.0	2.2
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 income before reclassifications	0.0	2.1
Amounts reclassified from AOCI	(67.9)	0.0
Net current period other comprehensive income/(loss)	(67.9)	2.1
Ending balance	$ 0.0	8.7
Hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		6.4
Other comprehensive income before reclassifications		(0.3)
Amounts reclassified from AOCI		(4.2)
Net current period other comprehensive income/(loss)		(4.5)
Ending balance		$ 1.9