Fair Value Measurements Of Plan Assets (Detail) (Pension Plans, Defined Benefit, USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	$ 455.6	[1]	$ 416.2	[1]	$ 355.7
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	8.8	[1]	6.7	[1]
Guaranteed Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	7.3	[1]	7.0	[1]
Equity Securities | US Large Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	132.4	[1]	117.8	[1]
Equity Securities | US Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	37.3	[1]	35.3	[1]
Equity Securities | US Small Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	46.7	[1]	45.8	[1]
Equity Securities | Foreign Equity Security
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	76.0	[1]	75.1	[1]
Fixed Income Securities | Diversified Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	121.4	[1],[2]	106.9	[1],[2]
Fixed Income Securities | Foreign Government Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	12.8	[1]	10.6	[1]
Fixed Income Securities | Foreign Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	12.9	[1]	11.0	[1]
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	122.0		111.3
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	7.7		0
Fair Value, Inputs, Level 1 | Guaranteed Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 1 | Equity Securities | US Large Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 1 | Equity Securities | US Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	37.3		35.3
Fair Value, Inputs, Level 1 | Equity Securities | US Small Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	46.7		45.8
Fair Value, Inputs, Level 1 | Equity Securities | Foreign Equity Security
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	30.3		30.2
Fair Value, Inputs, Level 1 | Fixed Income Securities | Diversified Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	0	[2]	0	[2]
Fair Value, Inputs, Level 1 | Fixed Income Securities | Foreign Government Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 1 | Fixed Income Securities | Foreign Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	333.6		304.9
Fair Value, Inputs, Level 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	1.1		6.7
Fair Value, Inputs, Level 2 | Guaranteed Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	7.3		7.0
Fair Value, Inputs, Level 2 | Equity Securities | US Large Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	132.4		117.8
Fair Value, Inputs, Level 2 | Equity Securities | US Mid Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 2 | Equity Securities | US Small Cap
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	0		0
Fair Value, Inputs, Level 2 | Equity Securities | Foreign Equity Security
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	45.7		44.9
Fair Value, Inputs, Level 2 | Fixed Income Securities | Diversified Bond Fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	121.4	[2]	106.9	[2]
Fair Value, Inputs, Level 2 | Fixed Income Securities | Foreign Government Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	12.8		10.6
Fair Value, Inputs, Level 2 | Fixed Income Securities | Foreign Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets fair value	$ 12.9		$ 11.0

[1] There were no plan assets categorized as Level 3 at December 31, 2014 and 2013, respectively.

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