Financial Assets and Liabilities Subject to Recurring Fair Value Measurements (Detail) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	$ 947.8	$ 910.1
Derivative assets	2.1	2.4
Derivative liabilities	108.8	110.5
Domestic Nontaxable Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	296.7	294.4
US Treasury and Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	1.5	1.9
Domestic Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	29.2	27.5
Foreign Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	150.1	148.3
Foreign Government Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	390.2	367.1
Other Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	80.1	70.9
Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	1.5	1.4
Derivative liabilities	35.2	33.3
Cross Currency Swap
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.1	0.8
Derivative liabilities	72.9	74.7
Foreign Exchange Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.5	0.2
Derivative liabilities	0.7	2.5
Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	0.6	1.9
Level 1 | US Treasury and Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	0.6	1.9
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	947.2	908.2
Derivative assets	2.1	2.4
Derivative liabilities	108.8	110.5
Level 2 | Domestic Nontaxable Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	296.7	294.4
Level 2 | US Treasury and Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	0.9
Level 2 | Domestic Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	29.2	27.5
Level 2 | Foreign Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	150.1	148.3
Level 2 | Foreign Government Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	390.2	367.1
Level 2 | Other Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable debt securities	80.1	70.9
Level 2 | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	1.5	1.4
Derivative liabilities	35.2	33.3
Level 2 | Cross Currency Swap
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.1	0.8
Derivative liabilities	72.9	74.7
Level 2 | Foreign Exchange Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	0.5	0.2
Derivative liabilities	$ 0.7	$ 2.5