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Goodwill - Summary of Goodwill (Detail) - USD ($)
$ in Millions
Jun. 30, 2015
Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]    
Gross cost $ 504.9 $ 512.6
Accumulated impairment losses (236.5) (236.5)
Net book amount $ 268.4 $ 276.1