Accumulated Other Comprehensive Income (Loss) - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Benefit plans expenses reclassified from accumulated OCI to income	$ 3.8	$ 7.4	$ 6.8
Deferred gains and losses on derivatives reclassified from accumulated OCI to income	$ 6.3	$ 18.2	$ 5.9