Retirement Plans - Components of Net Pension and Postretirement Benefits (Income) Expense and Total (Income) Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Settlements		$ 95.7
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.9	2.2	$ 2.2
Interest cost	178.2	194.5	178.2
Expected return on plan assets	(246.0)	(259.0)	(241.9)
Amortization of prior service credit	0.0	0.0	0.0
Amortization of actuarial loss	40.5	31.9	50.5
Settlements	0.2	95.7	0.7
Net periodic benefit (income) expense	$ (25.2)	$ 65.3	$ (10.3)
Discount rate	4.10%	5.00%	4.20%
Rate of compensation increase	0.20%	0.20%	0.30%
Expected return on plan assets	7.30%	7.60%	7.90%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4.7	$ 4.6	$ 7.3
Interest cost	16.0	16.8	16.2
Expected return on plan assets	(13.1)	(13.9)	(11.8)
Amortization of prior service credit	(26.9)	(25.8)	(19.7)
Amortization of actuarial loss	0.0	0.0	0.0
Settlements	0.0	0.0	0.0
Net periodic benefit (income) expense	$ (19.3)	$ (18.3)	$ (8.0)
Discount rate	3.90%	4.50%	3.90%
Expected return on plan assets	7.30%	7.30%	7.30%