Derivative Instruments- Impact of Derivative Instruments on Income Statement (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Fair Value Hedging | Interest Rate Contract | Net Interest Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in income on derivatives	$ 75	$ 39	$ 127
Gain or (loss) recognized in hedged item	(71)	(48)	(127)
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in OCI on derivative (effective portion)	185	932	342
Gain or (loss) reclassified from accumulated OCI into income (effective portion)	184	936	336
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing)	0.1	0	0.1
Cash Flow Hedging | Foreign Exchange Contract | Net Interest Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in OCI on derivative (effective portion)	2	(3)	(2)
Gain or (loss) reclassified from accumulated OCI into income (effective portion)	1	(4)	(5)
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing)	0	0	0
Cash Flow Hedging | Foreign Exchange Contract | Other Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in OCI on derivative (effective portion)	2	(3)	3
Gain or (loss) reclassified from accumulated OCI into income (effective portion)	0	1	1
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing)	0.1	0	0.1
Cash Flow Hedging | Foreign Exchange Contract | Trading Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in OCI on derivative (effective portion)	183	939	342
Gain or (loss) reclassified from accumulated OCI into income (effective portion)	183	939	342
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing)	0	0	0
Cash Flow Hedging | Foreign Exchange Contract | Salary Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in OCI on derivative (effective portion)	(2)	(1)	(1)
Gain or (loss) reclassified from accumulated OCI into income (effective portion)	0	0	(2)
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing)	0	0	0
Net Investment Hedging | Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in OCI on derivative (effective portion)	167	(19)	(139)
Gain or (loss) reclassified from accumulated OCI into income (effective portion)	0	0	0
Net Investment Hedging | Foreign Exchange Contract | Other Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (loss) recognized in income on derivatives (ineffectiveness portion and amount excluded from effectiveness testing)	$ (0.1)	$ 1.7	$ (0.1)