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	Jun. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 520.8
Equity securities	9.7
Mortgage loans	4.6
Other investments	0.9
Debt	1,032.0
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	520.8
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	9.7
Mortgage loans	4.6
Other investments	0.9
Debt	$ 1,032.0