Retirement Plans - Allocation of Plan Assets, Pension Plan (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Private Equity | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 45.1	$ 47.3	$ 43.4
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	3,595.1	3,841.8	$ 3,707.3
Pension Benefits | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,047.8	1,085.4
Pension Benefits | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	2,502.2	2,709.1
Pension Benefits | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	45.1	47.3
Pension Benefits | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	136.2	66.4
Pension Benefits | Cash and Cash Equivalents | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	105.5	44.1
Pension Benefits | Cash and Cash Equivalents | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	30.7	22.3
Pension Benefits | Cash and Cash Equivalents | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,534.0	1,751.7
Pension Benefits | Equity | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	904.3	997.5
Pension Benefits | Equity | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	629.7	754.2
Pension Benefits | Equity | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,713.9	1,830.6
Pension Benefits | Fixed Income | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	36.6	43.0
Pension Benefits | Fixed Income | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1,677.3	1,787.6
Pension Benefits | Fixed Income | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Derivatives and Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	19.4	12.8
Pension Benefits | Derivatives and Other | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	1.4	0.8
Pension Benefits | Derivatives and Other | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	18.0	12.0
Pension Benefits | Derivatives and Other | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	146.5	133.0
Pension Benefits | Real Estate | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Real Estate | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	146.5	133.0
Pension Benefits | Real Estate | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Private Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	45.1	47.3
Pension Benefits | Private Equity | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Private Equity | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	0.0	0.0
Pension Benefits | Private Equity | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the company's benefit plan assets	$ 45.1	$ 47.3