Financial Assets and Liabilities Subject to Recurring Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	$ 89.2	$ 48.0
Derivative liabilities	48.5	68.6
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	1,272.0	1,267.5
Derivative assets	89.2	48.0
Derivative liabilities	48.5	68.6
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	363.4	216.1
Fair Value, Measurements, Recurring | U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	81.5	78.2
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	8.0	5.5
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	532.0	609.3
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	194.1	217.5
Fair Value, Measurements, Recurring | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	93.0	140.9
Fair Value, Measurements, Recurring | Cross currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	81.7	40.9
Derivative liabilities	31.1	42.1
Fair Value, Measurements, Recurring | Interest-rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	1.0	5.4
Derivative liabilities	14.6	25.6
Fair Value, Measurements, Recurring | Foreign-exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	6.5	1.7
Derivative liabilities	2.8	0.9
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	7.7	5.2
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	7.7	5.2
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable debt securities	1,264.3	1,262.3
Derivative assets	89.2	48.0
Derivative liabilities	48.5	68.6
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	363.4	216.1
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	81.5	78.2
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	0.3	0.3
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	532.0	609.3
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	194.1	217.5
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	93.0	140.9
Level 2 | Fair Value, Measurements, Recurring | Cross currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	81.7	40.9
Derivative liabilities	31.1	42.1
Level 2 | Fair Value, Measurements, Recurring | Interest-rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	1.0	5.4
Derivative liabilities	14.6	25.6
Level 2 | Fair Value, Measurements, Recurring | Foreign-exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	6.5	1.7
Derivative liabilities	$ 2.8	$ 0.9