Financial Assets and Liabilities Subject to Recurring Fair Value Measurements (Detail) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	$ 955.9	$ 910.1
Derivative assets	2.9	2.4
Derivative liabilities	115.1	110.5
U.S. tax-exempt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	302.3	294.4
U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	28.2	27.5
U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	1.2	1.9
Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	393.5	367.1
Non-U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	151.4	148.3
Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	79.3	70.9
Interest-rate swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	1.1	1.4
Derivative liabilities	38.5	33.3
Cross currency swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.9	0.8
Derivative liabilities	76.1	74.7
Foreign-exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.9	0.2
Derivative liabilities	0.5	2.5
Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	0.5	1.9
Level 1 | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	0.5	1.9
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	955.4	908.2
Derivative assets	2.9	2.4
Derivative liabilities	115.1	110.5
Level 2 | U.S. tax-exempt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	302.3	294.4
Level 2 | U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	28.2	27.5
Level 2 | U.S. government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	0.7
Level 2 | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	393.5	367.1
Level 2 | Non-U.S. corporate securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	151.4	148.3
Level 2 | Other debt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	79.3	70.9
Level 2 | Interest-rate swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	1.1	1.4
Derivative liabilities	38.5	33.3
Level 2 | Cross currency swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.9	0.8
Derivative liabilities	76.1	74.7
Level 2 | Foreign-exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.9	0.2
Derivative liabilities	$ 0.5	$ 2.5