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		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Interest rate swaps [Member] | Interest expense [Member]
Derivatives And Hedging Activities [Line Items]
Gain / (Loss) on Instrument	$ (1.6)	$ 2.7	$ (15.7)	$ 7.8
Gain / (Loss) on Hedged Item	$ 1.6	$ (2.7)	$ 15.7	$ (7.8)