Financial Assets and Liabilities Subject to Recurring Fair Value Measurements (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	$ 51.7	$ 118.4
Derivative liabilities	97.1	49.3
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	1,216.0	1,140.9
Derivative assets	51.7	118.4
Derivative liabilities	97.1	49.3
Fair Value, Measurements, Recurring | Cross currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	43.2	102.7
Derivative liabilities	84.1	37.1
Fair Value, Measurements, Recurring | Interest-rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	4.6	7.0
Derivative liabilities	7.2	9.3
Fair Value, Measurements, Recurring | Foreign-exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3.9	8.7
Derivative liabilities	5.8	2.9
Fair Value, Measurements, Recurring | U.S. tax-exempt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	522.0	595.0
Fair Value, Measurements, Recurring | U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	58.9	47.8
Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	12.2	16.0
Fair Value, Measurements, Recurring | Non-U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	397.9	308.0
Fair Value, Measurements, Recurring | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	97.2	98.2
Fair Value, Measurements, Recurring | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	127.8	75.9
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	12.2	15.4
Derivative assets	0.0	0.0
Derivative liabilities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | Cross currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0.0	0.0
Derivative liabilities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | Interest-rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0.0	0.0
Derivative liabilities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | Foreign-exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0.0	0.0
Derivative liabilities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | U.S. tax-exempt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	12.2	15.4
Level 1 | Fair Value, Measurements, Recurring | Non-U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0.0	0.0
Level 1 | Fair Value, Measurements, Recurring | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0.0	0.0
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	1,203.8	1,125.5
Derivative assets	51.7	118.4
Derivative liabilities	97.1	49.3
Level 2 | Fair Value, Measurements, Recurring | Cross currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	43.2	102.7
Derivative liabilities	84.1	37.1
Level 2 | Fair Value, Measurements, Recurring | Interest-rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	4.6	7.0
Derivative liabilities	7.2	9.3
Level 2 | Fair Value, Measurements, Recurring | Foreign-exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3.9	8.7
Derivative liabilities	5.8	2.9
Level 2 | Fair Value, Measurements, Recurring | U.S. tax-exempt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	522.0	595.0
Level 2 | Fair Value, Measurements, Recurring | U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	58.9	47.8
Level 2 | Fair Value, Measurements, Recurring | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	0.0	0.6
Level 2 | Fair Value, Measurements, Recurring | Non-U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	397.9	308.0
Level 2 | Fair Value, Measurements, Recurring | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	97.2	98.2
Level 2 | Fair Value, Measurements, Recurring | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	$ 127.8	$ 75.9