Types and Classifications of Derivative Instruments Designated as Hedges (Detail) (Asset And Liability Management, USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Notional Value	$ 7,015.4	$ 6,884.8
Fair Value Asset	215.4	251.7
Fair Value Liability	53.6	48.7
FAIR VALUE HEDGES | Senior Notes and Long- Term Subordinated Debt | Interest Rate Swaps
Derivative [Line Items]
Notional Value	1,250.0	1,250.0
Fair Value Asset	138.4	112.8
Fair Value Liability	2.0	2.0
FAIR VALUE HEDGES | Available for Sale Investment Securities | Interest Rate Swaps
Derivative [Line Items]
Notional Value	2,815.7	2,859.5
Fair Value Asset	6.0	12.7
Fair Value Liability	26.9	28.5
CASH FLOW HEDGES | Forecasted Foreign Currency Denominated Transactions | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	340.5	344.9
Fair Value Asset	8.8	6.0
Fair Value Liability	24.4	14.8
CASH FLOW HEDGES | Available for Sale Investment Securities | Interest Rate Swaps
Derivative [Line Items]
Notional Value	10.0	10.0
CASH FLOW HEDGES | Available for Sale Investment Securities | Interest Rate Option Contracts
Derivative [Line Items]
Notional Value	725.0	625.0
Fair Value Asset	4.5	1.3
Net Investment Hedges | Net Investments in Non-U.S. Affiliates | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	1,874.2	1,795.4
Fair Value Asset	57.7	118.9
Fair Value Liability	$ 0.3	$ 3.4