Types and Classifications of Derivative Instruments Designated as Hedges (Detail) (Asset And Liability Management, USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional Value	$ 6,478.4	$ 6,637.4
Fair Value Asset	169.0	140.7
Fair Value Liability	77.1	114.6
FAIR VALUE HEDGES | Senior Notes and Long- Term Subordinated Debt | Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	900.0	900.0
Fair Value Asset	110.9	126.3
Fair Value Liability	0.1	0.2
FAIR VALUE HEDGES | Available for Sale Investment Securities | Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	3,495.7	3,617.0
Fair Value Asset	5.7	3.4
Fair Value Liability	60.9	75.1
CASH FLOW HEDGES | Forecasted Foreign Currency Denominated Transactions | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	531.7	669.0
Fair Value Asset	5.9	8.7
Fair Value Liability	15.4	11.5
NET INVESTMENT HEDGES | Net Investments in Non-U.S. Affiliates | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	1,551.0	1,451.4
Fair Value Asset	46.5	2.3
Fair Value Liability	$ 0.7	$ 27.8