Employee Benefits - Components of Estimated Net Pension and Other Postretirement Benefit Plan (Income) Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension (income) expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.5	$ 0.7	$ 1.6	$ 2.3
Interest cost	49.7	44.6	146.3	133.7
Expected return on plan assets	(65.9)	(60.6)	(195.1)	(181.8)
Amortization, net	7.8	12.4	24.1	37.6
Settlements	0	0.8	0	0.8
Net pension income	(7.9)	(2.1)	(23.1)	(7.4)
Other postretirement benefits plan (income) expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1	1.8	3.4	5.5
Interest cost	4.2	4.1	12.6	12.2
Expected return on plan assets	(2.9)	(3.0)	(9.1)	(8.9)
Amortization, net	(6.4)	(4.9)	(19.3)	(14.8)
Net other postretirement benefits plan income	$ (4.0)	$ (2.0)	$ (12.4)	$ (6.0)