Other Comprehensive Income/(Loss) (Details) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 EUR (€)	Dec. 31, 2019 EUR (€)
Other comprehensive income/(loss), net of tax:
Currency translation differences on investments in foreign subsidiaries	$ 182.7	$ 155.6	$ (327.1)
Actuarial gain/(loss) related to employee benefit plans	(6.3)	(10.8)	(13.0)
Other comprehensive income/(loss), net of tax	6.4	2.9	(0.5)
Other comprehensive income/(loss)	182.8	147.7	(340.6)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	14,318.3	8,936.2	8,955.6
Other comprehensive income/(loss), net of tax	182.8	147.7	(340.6)
Ending balance	14,808.9	14,318.3	8,936.2
Currency translation gains (losses) on investments in foreign subsidiaries	(2.4)	(6.5)	10.3
Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			8,955.6
Foreign currency translation
Other comprehensive income/(loss), net of tax:
Currency translation differences on investments in foreign subsidiaries	182.7	155.6	(327.1)
Actuarial gain/(loss) related to employee benefit plans	0.0	0.0	0.0
Other comprehensive income/(loss), net of tax	0.0	0.0	0.0
Other comprehensive income/(loss)	182.7	155.6	(327.1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(462.0)	(617.6)	(290.5)
Other comprehensive income/(loss), net of tax	182.7	155.6	(327.1)
Ending balance	(279.3)	(462.0)	(617.6)
Foreign currency translation | Adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			0.0
Foreign currency translation | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(290.5)
Employee benefit plans
Other comprehensive income/(loss), net of tax:
Currency translation differences on investments in foreign subsidiaries	0.0	0.0	0.0
Actuarial gain/(loss) related to employee benefit plans	(6.3)	(10.8)	(13.0)
Other comprehensive income/(loss), net of tax	6.4	2.4	5.0
Other comprehensive income/(loss)	0.1	(8.4)	(8.0)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(126.1)	(117.7)	(109.7)
Other comprehensive income/(loss), net of tax	0.1	(8.4)	(8.0)
Ending balance	(126.0)	(126.1)	(117.7)
Employee benefit plans | Adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			0.0
Employee benefit plans | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(109.7)
Equity method investments
Other comprehensive income/(loss), net of tax:
Currency translation differences on investments in foreign subsidiaries	0.0	0.0	0.0
Actuarial gain/(loss) related to employee benefit plans	0.0	0.0	0.0
Other comprehensive income/(loss), net of tax	0.0	0.1	(4.3)
Other comprehensive income/(loss)	0.0	0.1	(4.3)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.1	0.0	4.3
Other comprehensive income/(loss), net of tax	0.0	0.1	(4.3)
Ending balance	0.1	0.1	0.0
Equity method investments | Adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			0.0
Equity method investments | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			4.3
Available-for-sale investments
Other comprehensive income/(loss), net of tax:
Currency translation differences on investments in foreign subsidiaries	0.0	0.0	0.0
Actuarial gain/(loss) related to employee benefit plans	0.0	0.0	0.0
Other comprehensive income/(loss), net of tax	0.0	0.4	(1.2)
Other comprehensive income/(loss)	0.0	0.4	(1.2)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.7	0.3	4.7
Other comprehensive income/(loss), net of tax	0.0	0.4	(1.2)
Ending balance	0.7	0.7	0.3
Available-for-sale investments | Adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(3.2)
Available-for-sale investments | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			1.5
Accumulated Other Comprehensive Income
Other comprehensive income/(loss), net of tax:
Other comprehensive income/(loss)	182.8	147.7	(340.6)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(587.3)	(735.0)	(391.2)
Other comprehensive income/(loss), net of tax	182.8	147.7	(340.6)
Ending balance	(404.5)	(587.3)	(735.0)
Accumulated Other Comprehensive Income | Adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(3.2)
Accumulated Other Comprehensive Income | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ (394.4)
Designated as Hedging Instrument
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Intercompany debt	$ 174.5	$ 172.1		€ 130	€ 130