Allocation of Plan Assets, Pension Plan (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Private Equity Funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 47.3	$ 43.4	$ 38.9
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	3,841.8	3,707.3	3,215.3
Pension Plans, Defined Benefit | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,085.4	2,149.3
Pension Plans, Defined Benefit | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	2,709.1	1,514.6
Pension Plans, Defined Benefit | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	47.3	43.4
Pension Plans, Defined Benefit | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	66.4	79.6
Pension Plans, Defined Benefit | Cash and Cash Equivalents | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	44.1	51.6
Pension Plans, Defined Benefit | Cash and Cash Equivalents | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	22.3	28.0
Pension Plans, Defined Benefit | Cash and Cash Equivalents | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,751.7	2,658.7
Pension Plans, Defined Benefit | Equity Funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	997.5	1,839.3
Pension Plans, Defined Benefit | Equity Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	754.2	819.4
Pension Plans, Defined Benefit | Equity Funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,830.6	795.3
Pension Plans, Defined Benefit | Fixed Income Funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	43.0	255.0
Pension Plans, Defined Benefit | Fixed Income Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,787.6	540.3
Pension Plans, Defined Benefit | Fixed Income Funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Derivative
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	12.8	3.9
Pension Plans, Defined Benefit | Derivative | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.8	3.4
Pension Plans, Defined Benefit | Derivative | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	12.0	0.5
Pension Plans, Defined Benefit | Derivative | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	133.0	126.4
Pension Plans, Defined Benefit | Real Estate | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Real Estate | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	133.0	126.4
Pension Plans, Defined Benefit | Real Estate | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	47.3	43.4
Pension Plans, Defined Benefit | Private Equity Funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Private Equity Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets
Pension Plans, Defined Benefit | Private Equity Funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 47.3	$ 43.4