Types and Classifications of Risk Management Derivative Instruments Not Formally Designated as Hedges, Including Notional and Fair Values (Detail) (Nondesignated, USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Notional Value	$ 990.8	$ 335.6
Fair Value Asset	10.2	4.5
Fair Value Liability	5.1	3.2
Credit Default Swap Contracts | Commercial Loans and Loan Commitments
Derivative [Line Items]
Notional Value	65.5	60.5
Fair Value Asset		0.7
Fair Value Liability	1.1	0.1
Foreign Exchange Contracts | Net Investments in Non-U.S. Affiliates
Derivative [Line Items]
Notional Value	767.8	63.5
Fair Value Asset	8.4	0.4
Fair Value Liability	3.3	0.2
Foreign Exchange Contracts | Forecasted Foreign Currency Denominated Transactions
Derivative [Line Items]
Notional Value		127.3
Fair Value Asset		2.1
Fair Value Liability		2.6
Foreign Exchange Contracts | Commercial Loans
Derivative [Line Items]
Notional Value	157.5	84.3
Fair Value Asset	1.8	1.3
Fair Value Liability	$ 0.7	$ 0.3