Derivative Instruments and Hedging Activities - Derivative Instruments Designated as Fair Value Hedges (Detail) (Interest Rate Swaps [Member], Interest Expense [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Rate Swaps [Member] | Interest Expense [Member]
Derivatives And Hedging Activities [Line Items]
Gain/(Loss) on Instrument	$ 14.7	$ (24.6)	$ 6.1
Gain/(Loss) on Hedged Item	$ (14.7)	$ 24.6	$ (6.1)