Amounts Recognized in Consolidated Balance Sheets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Other assets	$ 5.4	$ 4.5
Accrued benefit cost	(84.6)	(84.2)
Net amount recognized	(79.2)	(79.7)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit cost	(6.8)	(6.4)
Net amount recognized	$ (6.8)	$ (6.4)