Accumulated Other Comprehensive Income (Loss) - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Benefit plans expenses reclassified from accumulated OCI to income	$ 1.8	$ 1.6	$ 3.7	$ 3.3
Deferred gains and losses on derivatives reclassified from accumulated OCI to income	$ 6.2	$ 2.3	$ 12.3	$ 2.5