Allocation of Plan Assets, Postretirement Benefit Plan (Detail) (Other Postretirement Benefit Plans, Defined Benefit, USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 206.8	$ 187.1	$ 174.7
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	206.8	187.1
Cash and Cash Equivalents | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1.5	8.4
Equity Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	155.1	133.3
Fixed Income Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	39.6	35.9
Derivative | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 10.6	$ 9.5