Derivatives - Effect of Our Derivative Financial Instruments on Our Consolidated Statements of Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivatives in cash flow hedging relationships:
Loss recognized in Other Comprehensive Income (Loss) on derivatives	$ 9.7	$ (1.5)	$ 7.6	$ (3.6)
Interest expense [Member]
Derivatives in cash flow hedging relationships:
Loss reclassified from Accumulated Other Comprehensive Income (Loss) into income (effective portion)	3.0	4.5	7.0	8.4
Loss recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)	$ (3.2)		$ (2.7)