Derivative Instruments - Effect of Derivative Instruments in Consolidated Statements of Comprehensive Loss (Detail) (Interest rate contracts [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
Derivatives designated as hedging instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (gain) or loss reclassified from AOCL into net loss (effective portion)	$ 0	$ 6.9	$ 3.9	$ 21.2
Derivatives not designated as hedging instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized (gains)/losses	(34.1)	(6.2)	(100.6)	10.9
Derivative settlements	43.4	42.6	128.3	126.6
Total	$ 9.3	$ 36.4	$ 27.7	$ 137.5