Financial Assets and Liabilities Subject to Recurring Fair Value Measurements (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	$ 20.5	$ 56.3
Derivative liabilities	159.9	44.3
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	1,429.0	1,162.1
Derivative assets	20.5	56.3
Derivative liabilities	159.9	44.3
Fair Value, Measurements, Recurring \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	86.5	128.4
Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	1,342.5	1,033.7
Derivative assets	20.5	56.3
Derivative liabilities	159.9	44.3
Fair Value, Measurements, Recurring \| Cross currency swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	14.8	43.8
Derivative liabilities	77.6	13.5
Fair Value, Measurements, Recurring \| Cross currency swaps \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	14.8	43.8
Derivative liabilities	77.6	13.5
Fair Value, Measurements, Recurring \| Interest-rate swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	1.6	2.0
Derivative liabilities	38.5	17.5
Fair Value, Measurements, Recurring \| Interest-rate swaps \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	1.6	2.0
Derivative liabilities	38.5	17.5
Fair Value, Measurements, Recurring \| Foreign-exchange contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	4.1	10.5
Derivative liabilities	43.8	13.3
Fair Value, Measurements, Recurring \| Foreign-exchange contracts \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	4.1	10.5
Derivative liabilities	43.8	13.3
U.S. tax-exempt securities \| Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	392.4	320.2
U.S. tax-exempt securities \| Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	392.4	320.2
U.S. corporate securities \| Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	232.9	165.7
U.S. corporate securities \| Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	232.9	165.7
U.S. government and agency securities \| Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	94.4	129.3
U.S. government and agency securities \| Fair Value, Measurements, Recurring \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	86.5	128.4
U.S. government and agency securities \| Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	7.9	0.9
Non-U.S. corporate securities \| Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	411.5	349.8
Non-U.S. corporate securities \| Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	411.5	349.8
Non-U.S. government securities \| Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	77.5	72.4
Non-U.S. government securities \| Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	77.5	72.4
Other debt securities \| Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	220.3	124.7
Other debt securities \| Fair Value, Measurements, Recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities (amortized cost: 2020 - $1,409.7, 2019 - $1,154.0; allowance for credit losses: none)	$ 220.3	$ 124.7

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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