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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain/(Loss) Recognized in Income	$ 10.9	$ (20.0)	$ 44.1	$ 5.5
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	5.1	(16.4)	(21.9)	21.6
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	$ 5.8	$ (3.6)	$ 66.0	$ (16.1)