Fair Value Measurements Of Plan Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	$ 416.2	[1]	$ 355.7	[1]
Cash and Cash Equivalents
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	6.7	[1]	5.1	[1]
Guaranteed Insurance Contracts
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	7.0	[1]	5.8	[1]
Equity Securities | US Large Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	117.8	[1]	94.6	[1]
Equity Securities | US Mid Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	35.3	[1]	28.6	[1]
Equity Securities | US Small Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	45.8	[1]	38.7	[1]
Equity Securities | Foreign Equity Security
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	75.1	[1]	64.3	[1]
Fixed Income Securities | Diversified Bond Fund
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	106.9	[1],[2]	98.6	[1],[2]
Fixed Income Securities | Foreign Government Debt Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	10.6	[1]	9.8	[1]
Fixed Income Securities | Foreign Corporate Debt Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	11.0	[1]	10.2	[1]
Fair Value, Inputs, Level 1
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	111.3		95.1
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 1 | Guaranteed Insurance Contracts
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 1 | Equity Securities | US Large Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 1 | Equity Securities | US Mid Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	35.3		28.6
Fair Value, Inputs, Level 1 | Equity Securities | US Small Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	45.8		38.7
Fair Value, Inputs, Level 1 | Equity Securities | Foreign Equity Security
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	30.2		27.8
Fair Value, Inputs, Level 1 | Fixed Income Securities | Diversified Bond Fund
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0	[2]	0	[2]
Fair Value, Inputs, Level 1 | Fixed Income Securities | Foreign Government Debt Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 1 | Fixed Income Securities | Foreign Corporate Debt Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 2
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	304.9		260.6
Fair Value, Inputs, Level 2 | Cash and Cash Equivalents
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	6.7		5.1
Fair Value, Inputs, Level 2 | Guaranteed Insurance Contracts
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	7.0		5.8
Fair Value, Inputs, Level 2 | Equity Securities | US Large Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	117.8		94.6
Fair Value, Inputs, Level 2 | Equity Securities | US Mid Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 2 | Equity Securities | US Small Cap
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 2 | Equity Securities | Foreign Equity Security
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	44.9		36.5
Fair Value, Inputs, Level 2 | Fixed Income Securities | Diversified Bond Fund
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	106.9	[2]	98.6	[2]
Fair Value, Inputs, Level 2 | Fixed Income Securities | Foreign Government Debt Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	10.6		9.8
Fair Value, Inputs, Level 2 | Fixed Income Securities | Foreign Corporate Debt Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value [Line Items]
Plan assets fair value	$ 11.0		$ 10.2

[1] There were no plan assets categorized as Level 3 at December 31, 2013 and 2012, respectively.

[2] Diversified bond fund consists of U.S. Treasury bonds, mortgage backed securities, and corporate bonds.