Gains and Losses Recorded in Consolidated Statement of Income related to Fair Value Hedges (Detail) (Asset And Liability Management, FAIR VALUE HEDGES, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain/(Loss) Recognized in Income	$ (14.4)	$ 12.0	$ 78.3	$ 137.2
Available for Sale Investment Securities | Interest Rate Swap Contracts | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain/(Loss) Recognized in Income	(23.3)	(27.0)	(93.5)	(53.2)
Senior Notes and Long- Term Subordinated Debt | Interest Rate Swap Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain/(Loss) Recognized in Income	$ 8.9	$ 39.0	$ 171.8	$ 190.4