Components of Net Pension and Postretirement Benefits (Income) Expense and Total (Income) Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Curtailments			$ (3.7)
Loss on pension settlement	95.7
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.2	2.2	5.9
Interest cost	194.5	178.2	189.2
Expected return on plan assets	(259.0)	(241.9)	(262.6)
Amortization of prior service credit			0.6
Amortization of actuarial loss (gain)	31.9	50.5	32.1
Curtailments			(3.7)
Loss on pension settlement	95.7	0.7	1.1
Net periodic benefit (income) expense	65.3	(10.3)	(37.4)
Discount rate	5.00%	4.20%	4.90%
Rate of compensation increase	0.20%	0.30%	0.90%
Expected return on plan assets	7.60%	7.90%	8.40%
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	4.6	7.3	6.6
Interest cost	16.8	16.2	18.4
Expected return on plan assets	(13.9)	(11.8)	(13.9)
Amortization of prior service credit	(25.8)	(19.7)	(19.7)
Amortization of actuarial loss (gain)			(0.1)
Curtailments
Loss on pension settlement
Net periodic benefit (income) expense	$ (18.3)	$ (8.0)	$ (8.7)
Discount rate	4.50%	3.90%	4.80%
Rate of compensation increase			3.60%
Expected return on plan assets	7.30%	7.30%	7.60%