Estimated Fair Values of Financial Instruments Not Carried at Fair Value (Detail) (Estimate of Fair Value, Fair Value Disclosure, USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 691.0	$ 564.8
Equity securities	9.3	9.7
Other investments	14.7	16.6
Debt	1,116.7	995.2
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	691.0	564.8
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	9.3	9.7
Other investments	4.0	4.8
Debt	1,116.7	995.2
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments	$ 10.7	$ 11.8