Types and Classifications of Derivative Instruments Designated as Hedges (Detail) (Asset And Liability Management, USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Notional Value	$ 6,346.5	$ 5,759.6
Fair Value Asset	153.2	171.0
Fair Value Liability	88.0	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	135.1	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	2,797.0	2,172.0
Fair Value Asset	6.7	2.6
Fair Value Liability	45.4	46.8
CASH FLOW HEDGES | Forecasted Foreign Currency Denominated Transactions | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	983.8	932.9
Fair Value Asset	10.8	9.4
Fair Value Liability	15.5	27.2
NET INVESTMENT HEDGES | Net Investments in Non-U.S. Affiliates | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	1,465.7	1,554.7
Fair Value Asset	0.6	12.0
Fair Value Liability	$ 26.6	$ 1.5