Location and Amounts of Gains and Losses on Derivative Instrument Designated as Fair Value Hedge (Detail) (Interest rate swap contract, Interest Expense, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest rate swap contract | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
(Loss)/Gain Recognized on Swap	$ (4.3)	$ (4.4)	$ 1.2
Gain/(Loss) Recognized on Long-Term Debt	$ 4.3	$ 4.4	$ (1.2)