Amounts In Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 1,828.9	$ 1,574.3
Net transition obligation	0.2	0.2
Total	1,829.1	1,574.5
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	1.6	(9.1)
Net prior service credit	(68.0)	(87.8)
Total	$ (66.4)	$ (96.9)