Financial Assets and Liabilities Subject to Recurring Fair Value Measurements (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	$ 103.8	$ 94.7
Derivative liabilities	32.0	24.6
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	1,107.8	1,020.4
Derivative assets	103.8	94.7
Derivative liabilities	32.0	24.6
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	126.2	97.1
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable debt securities	981.6	923.3
Derivative assets	103.8	94.7
Derivative liabilities	32.0	24.6
Fair Value, Measurements, Recurring | Cross currency swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	80.8	75.4
Derivative liabilities	2.8	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	80.8	75.4
Derivative liabilities	2.8	11.2
Fair Value, Measurements, Recurring | Interest-rate swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	1.9	9.1
Derivative liabilities	24.0	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	1.9	9.1
Derivative liabilities	24.0	7.3
Fair Value, Measurements, Recurring | Foreign-exchange contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	21.1	10.2
Derivative liabilities	5.2	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	21.1	10.2
Derivative liabilities	5.2	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	318.4	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	318.4	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	162.6	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	162.6	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	127.1	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	126.2	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	0.9	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	305.4	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	305.4	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	65.3	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	65.3	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	129.0	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	$ 129.0	$ 122.0