Types and Classifications of Derivative Instruments Designated as Hedges (Detail) (Asset And Liability Management, USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Notional Value	$ 6,990.4	$ 5,759.6
Fair Value Asset	165.1	171.0
Fair Value Liability	112.4	76.0
FAIR VALUE HEDGES | Senior Notes and Long- Term Subordinated Debt | Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	1,100.0	1,100.0
Fair Value Asset	135.7	147.0
Fair Value Liability	0.5	0.5
FAIR VALUE HEDGES | Available for Sale Investment Securities | Interest Rate Swap Contracts
Derivative [Line Items]
Notional Value	3,535.2	2,172.0
Fair Value Asset	3.6	2.6
Fair Value Liability	76.7	46.8
CASH FLOW HEDGES | Forecasted Foreign Currency Denominated Transactions | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	805.7	932.9
Fair Value Asset	12.5	9.4
Fair Value Liability	14.9	27.2
NET INVESTMENT HEDGES | Net Investments in Non-U.S. Affiliates | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	1,549.5	1,554.7
Fair Value Asset	13.3	12.0
Fair Value Liability	$ 20.3	$ 1.5