Accumulated Other Comprehensive Income (Loss) - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Benefit plans expenses reclassified from accumulated OCI to income	$ 1.6	$ 1.2
Gain/(Loss), Reclassified from AOCI to Income	$ 7.4	$ 2.0