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Derivative Financial Instruments - Effect on Statement of Comprehensive Income and Statement of Income (Details) - Designated as Hedging Instrument - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivatives in Net Investment Hedging Relationship
Derivative [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Loss)	$ 0.3	$ 6.9	$ 13.8	$ 7.3
Gain Reclassified from Accumulated Other Comprehensive Loss into Earnings	0.1	(0.0)	0.4	0.1
Gain (Loss) Recognized in Earnings from Excluded Components	0.0	3.5	2.8	10.4
Derivatives in Net Investment Hedging Relationship | Forward contracts
Derivative [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Loss)	0.4	22.8	64.9	32.6
Gain Reclassified from Accumulated Other Comprehensive Loss into Earnings	0.1	(0.0)	0.4	0.1
Gain (Loss) Recognized in Earnings from Excluded Components	0.0	3.5	2.8	10.4
Derivatives in Net Investment Hedging Relationship | Put options
Derivative [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Loss)	0.0	(8.4)	(47.7)	(2.8)
Gain Reclassified from Accumulated Other Comprehensive Loss into Earnings	0.0	0.0	0.0	0.0
Gain (Loss) Recognized in Earnings from Excluded Components	0.0	0.0	0.0	0.0
Derivatives in Net Investment Hedging Relationship | Call options
Derivative [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Loss)	0.0	(7.5)	(1.3)	(22.5)
Gain Reclassified from Accumulated Other Comprehensive Loss into Earnings	0.0	0.0	0.0	0.0
Gain (Loss) Recognized in Earnings from Excluded Components	0.0	0.0	0.0	0.0
Cash Flow Hedging | Interest rate swap
Derivative [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Loss)	(0.1)	0.0	(2.1)	0.0
Gain Reclassified from Accumulated Other Comprehensive Loss into Earnings	0.0	0.0	0.0	0.0
Gain (Loss) Recognized in Earnings from Excluded Components	$ 0.0	$ 0.0	$ 0.0	$ 0.0

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Gain (Loss) On Derivative Used In Cash Flow Hedge And Net Investment Hedge, After Tax

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The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

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Amount, after tax and reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness, attributable to parent.

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Amount, before tax and adjustments, of gain (loss) from increase (decrease) in value of excluded component of derivative designated and qualifying as hedge. Adjustments include, but are not limited to, reclassifications for sale and settlement, and amounts recognized under systematic and rational method.

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Amount, after tax, of reclassification from accumulated other comprehensive income (AOCI) of gain (loss) from increase (decrease) in fair value of net investment hedge.

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