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, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional Value	$ 221.0	$ 1,232.3
Fair Value Asset	1.0	10.3
Fair Value Liability	2.2	4.0
Credit Default Swap Contracts | Commercial Loans and Loan Commitments
Derivative [Line Items]
Notional Value	25.0	42.5
Fair Value Liability	0.1	1.0
Foreign Exchange Contracts | Net Investments in Non-U.S. Affiliates
Derivative [Line Items]
Notional Value	54.3	1,051.8
Fair Value Asset	0.3	8.9
Fair Value Liability	0.3	2.3
Foreign Exchange Contracts | Forecasted Foreign Currency Denominated Transactions
Derivative [Line Items]
Notional Value	7.1	2.2
Fair Value Asset		0.1
Fair Value Liability	0.2
Foreign Exchange Contracts | Commercial Loans
Derivative [Line Items]
Notional Value	134.6	135.8
Fair Value Asset	0.7	1.3
Fair Value Liability	$ 1.6	$ 0.7