Gains and Losses Recorded in Consolidated Statements of Income Related to Fair Value Hedges (Detail) (Asset And Liability Management, FAIR VALUE HEDGES, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain/(Loss) Recognized in Income	$ 12.5	$ 20.4
Available for Sale Investment Securities | Interest Rate Swaps | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain/(Loss) Recognized in Income	(17.3)	(12.1)
Senior Notes and Long- Term Subordinated Debt | Interest Rate Swaps | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain/(Loss) Recognized in Income	$ 29.8	$ 32.5