Derivatives - Effect of Our Derivative Financial Instruments on Our Consolidated Statements of Operations (Detail) (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 in cash flow hedging relationships:
Gain (loss) recognized in Other Comprehensive Income (Loss) on derivatives	$ 0.3	$ (1.3)	$ 7.9	$ (4.9)
Interest
Derivatives in cash flow hedging relationships:
Loss reclassified from Accumulated Other Comprehensive Income (Loss) into income (effective portion)	2.0	4.6	9.0	13.0
Loss recognized in income on derivatives (ineffective portion and amount excluded from effectiveness testing)	$ (0.7)		$ (3.4)