Summary of Changes in Benefit Obligation and Plan Assets for Defined Benefit Pension and Postretirement Benefit Plans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Tax benefits related to changes in benefit obligation and plan assets which are also included in accumulated other comprehensive loss	$ 88.0	$ 70.2