Derivative Instruments (Detail) $ in Millions	Jun. 30, 2015 USD ($) item	Dec. 31, 2014 USD ($) item
Derivative
Number of Hedging instruments | item	0	0
Derivatives not designated as hedging instruments
Derivative
Notional Amount	$ 4,949.9	$ 4,344.7
Derivative Assets	52.8	53.2
Derivative Liabilities	50.7	52.9
Derivatives not designated as hedging instruments | Option contracts
Derivative
Notional Amount		1.9
Derivative Assets		0.4
Derivatives not designated as hedging instruments | Interest-Rate Contracts
Derivative
Notional Amount	3,955.7	3,531.8
Derivative Assets	44.0	45.5
Derivative Liabilities	44.2	46.0
Derivatives not designated as hedging instruments | Interest-Rate Swaps
Derivative
Notional Amount	3,431.5	3,094.5
Derivative Assets	43.6	44.7
Derivative Liabilities	43.9	45.2
Derivatives not designated as hedging instruments | Interest Rate Caps, Floors and Collars
Derivative
Notional Amount	524.2	437.3
Derivative Assets	0.4	0.8
Derivative Liabilities	0.3	0.8
Derivatives not designated as hedging instruments | Spot and forward contracts
Derivative
Notional Amount	983.4	802.7
Derivative Assets	6.6	6.1
Derivative Liabilities	6.2	6.6
Derivatives not designated as hedging instruments | Foreign Exchange Contracts
Derivative
Notional Amount	989.4	808.7
Derivative Assets	6.9	6.4
Derivative Liabilities	6.5	6.9
Derivatives not designated as hedging instruments | Foreign Exchange Contracts | Options purchased | Purchase
Derivative
Notional Amount	3.0	3.0
Derivative Assets	0.1	0.1
Derivative Liabilities	0.1	0.1
Derivatives not designated as hedging instruments | Foreign Exchange Contracts | Options purchased | Sale
Derivative
Notional Amount	3.0	3.0
Derivative Assets	0.2	0.2
Derivative Liabilities	0.2	0.2
Equity Warrants | Derivatives not designated as hedging instruments
Derivative
Notional Amount	4.8	2.3
Derivative Assets	$ 1.9	$ 0.9