Allocation of Plan Assets, Pension Plan (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 3,215.3	$ 2,849.6	$ 3,029.6
Pension Plans, Defined Benefit | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	56.9	65.2
Pension Plans, Defined Benefit | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	2,169.0	1,857.0
Pension Plans, Defined Benefit | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	828.0	779.1
Pension Plans, Defined Benefit | Derivative
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	8.9	6.9
Pension Plans, Defined Benefit | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	113.6	111.3
Pension Plans, Defined Benefit | Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	38.9	30.1
Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	2,155.8	1,873.3
Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	27.4	43.4
Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,887.4	1,604.4
Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	240.5	214.8
Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Derivative
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.5	3.6
Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets		7.1
Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,020.6	946.2
Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	29.5	21.8
Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	281.6	252.6
Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	587.5	564.3
Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Derivative
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	8.4	3.3
Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	113.6	104.2
Fair Value, Inputs, Level 3 | Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	38.9	30.1	15.5
Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	38.9	30.1
Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 38.9	$ 30.1