Defined Benefit Plans - Pension Assets by Major Category of Plan Assets and Type of Fair Value Measurement (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	$ 608.2	$ 583.8
Group annuity/insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	21.8	21.2
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	9.1	8.1
Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	282.6	278.6
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	248.0	232.6
Multi-strategy hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	21.6	20.5
Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	25.1	22.8
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	539.7	519.3
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	9.1	8.1
Level 2 | Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	282.6	278.6
Level 2 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	248.0	232.6
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	68.5	64.5
Level 3 | Group annuity/insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	21.8	21.2
Level 3 | Multi-strategy hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	21.6	20.5
Level 3 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value asset measurements	$ 25.1	$ 22.8