Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at Beginning of Period	$ (863.3)	$ (490.4)	$ (545.0)
Change in comprehensive income	(165.9)	(372.9)	54.6
Balance at End of Period	(1,029.2)	(863.3)	(490.4)
Fair Value Of Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at Beginning of Period	(1.1)	(1.8)	(2.1)
Change in comprehensive income	0.5	0.7	0.3
Balance at End of Period	(0.6)	(1.1)	(1.8)
Pension and Other Postretirement Benefit Plan Cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at Beginning of Period	(907.5)	(604.4)	(646.4)
Change in comprehensive income	(177.6)	(303.1)	42.0
Balance at End of Period	(1,085.1)	(907.5)	(604.4)
Accumulated Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at Beginning of Period	45.3	115.8	103.5
Change in comprehensive income	11.2	(70.5)	12.3
Balance at End of Period	$ 56.5	$ 45.3	$ 115.8