Ineffectiveness Related to Derivatives and Hedging Relationships Recorded in Income (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	$ (0.7)		$ (8.4)
Fair Value Hedge of Securities
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	0.7		(4.0)
Fair Value Hedge of Deposits and Long-Term Debt
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	(1.4)		(4.2)
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	0.1		(0.1)
Other
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	$ (0.1)	[1]	$ (0.1)	[1]

[1] Includes ineffectiveness recorded on foreign exchange hedges.