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	Mar. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Notional Value	$ 317.5	$ 335.6
Fair Value Asset	3.2	4.5
Fair Value Liability	3.7	3.2
Credit Default Swap Contracts | Commercial Loans and Loan Commitments
Derivative [Line Items]
Notional Value	60.5	60.5
Fair Value Asset		0.7
Fair Value Liability	0.2	0.1
Foreign Exchange Contracts | Net Investments in Non-U.S. Affiliates
Derivative [Line Items]
Notional Value	47.9	63.5
Fair Value Asset	0.1	0.4
Fair Value Liability	0.4	0.2
Foreign Exchange Contracts | Forecasted Foreign Currency Denominated Transactions
Derivative [Line Items]
Notional Value	67.8	127.3
Fair Value Asset	2.2	2.1
Fair Value Liability	2.4	2.6
Foreign Exchange Contracts | Commercial Loans
Derivative [Line Items]
Notional Value	141.3	84.3
Fair Value Asset	0.9	1.3
Fair Value Liability	$ 0.7	$ 0.3