Net Amounts Recognized, or Funded Status of Pension and Other Postretirement Benefit Plans (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Amounts recognized in the statements of financial position consist of:
Long-term liabilities	$ (176.4)	$ (129.0)
Pension Benefits
Amounts recognized in the statements of financial position consist of:
Prepaid pension asset		4.0
Current liabilities	(3.8)	(3.8)
Long-term liabilities	(159.3)	(108.3)
Net amount recognized	(163.1)	(108.1)
Other Benefits
Amounts recognized in the statements of financial position consist of:
Long-term liabilities	(10.6)	(14.6)
Net amount recognized	$ (10.6)	$ (14.6)