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	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Interest Rate Swaps [Member] | Interest Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on Instrument	$ 7.2	$ 5.1
Loss on Hedged Item	$ (7.2)	$ (5.1)