Components of Net Pension and Postretirement Benefits (Income) Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Curtailments	$ (3.7)	$ (38.7)	$ (0.4)
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	5.9	86.6	80.4
Interest cost	189.2	192.0	184.0
Expected return on plan assets	(262.6)	(266.4)	(258.7)
Amortization of prior service credit	0.6	(4.4)	(1.9)
Amortization of actuarial loss (gain)	32.1	50.1	29.7
Curtailments	(3.7)	(38.7)	(0.4)
Settlements	1.1
Net periodic benefit (income) expense	(37.4)	19.2	33.1
Discount rate	4.90%	5.50%	6.00%
Rate of compensation increase	0.90%	4.00%	4.00%
Expected return on plan assets	8.40%	8.40%	8.30%
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	6.6	8.2	12.2
Interest cost	18.4	22.7	28.4
Expected return on plan assets	(13.9)	(14.8)	(15.5)
Amortization of prior service credit	(19.7)	(12.5)	(10.8)
Amortization of actuarial loss (gain)	(0.1)	0.1	1.3
Net periodic benefit (income) expense	$ (8.7)	$ 3.7	$ 15.6
Discount rate	4.80%	5.20%	5.70%
Rate of compensation increase	3.60%	3.60%	4.00%
Expected return on plan assets	7.60%	7.60%	7.60%