Financial Assets and Liabilities Subject to Recurring Fair Value Measurements (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	$ 68.0	$ 94.7
Derivative liabilities	26.5	24.6
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	1,081.6	1,020.4
Derivative assets	68.0	94.7
Derivative liabilities	26.5	24.6
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	111.0	97.1
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	970.6	923.3
Derivative assets	68.0	94.7
Derivative liabilities	26.5	24.6
Fair Value, Measurements, Recurring | Cross currency swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	57.6	75.4
Derivative liabilities	7.5	11.2
Fair Value, Measurements, Recurring | Cross currency swaps | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	57.6	75.4
Derivative liabilities	7.5	11.2
Fair Value, Measurements, Recurring | Interest-rate swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	5.2	9.1
Derivative liabilities	9.8	7.3
Fair Value, Measurements, Recurring | Interest-rate swaps | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	5.2	9.1
Derivative liabilities	9.8	7.3
Fair Value, Measurements, Recurring | Foreign-exchange contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	5.2	10.2
Derivative liabilities	9.2	6.1
Fair Value, Measurements, Recurring | Foreign-exchange contracts | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	5.2	10.2
Derivative liabilities	9.2	6.1
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	304.9	325.1
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	304.9	325.1
U.S. corporate securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	163.4	147.4
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	163.4	147.4
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	111.0	98.7
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	111.0	97.1
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		1.6
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	302.8	271.3
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	302.8	271.3
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	74.4	55.9
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	74.4	55.9
Other debt securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	125.1	122.0
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	$ 125.1	$ 122.0