Financial Instruments and Fair Value Measurements - Derivative Activity (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Interest Rate Swaps [Member]
Derivative [Line Items]
Notional amounts at January 1	$ 1,496.5	$ 268.1
New contracts	444.2
Acquired contracts	71.0	1,337.3
Matured or expired contracts	(460.0)	(9.6)
Notional amounts at September 30	1,551.7	1,595.8
Interest Rate Caps [Member]
Derivative [Line Items]
Acquired contracts		25.7
Notional amounts at September 30		$ 25.7