Postretirement Health Care Plan Status (Detail) (Other Postretirement Plan, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Accumulated Postretirement Benefit Obligation	$ 33.4	$ 31.2	$ 30.6
Retirees and Dependents
Defined Benefit Plan Disclosure [Line Items]
Accumulated Postretirement Benefit Obligation	25.0	22.5
Actives Eligible for Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated Postretirement Benefit Obligation	$ 8.4	$ 8.7