Derivative Instruments- Ineffectiveness Related to Derivatives and Hedging Relationships Recorded in Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	$ 4.3		$ (7.4)		$ (0.1)
Fair Value Hedge of Securities
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	4.6		(1.6)		3.4
Fair Value Hedge of Deposits and Long-Term Debt
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	(0.3)		(7.5)		(3.5)
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	0.1		0		0.1
Other
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness related to derivatives and hedging relationships	$ (0.1)	[1]	$ 1.7	[1]	$ (0.1)	[1]

[1] Includes ineffectiveness recorded on foreign exchange hedges.