Fair Value Measurement- Quantitative Information about Level 3 Fair Value Measurements of Liabilities (Detail) (Fair Value, Measurements, Recurring, Level 3, USD $) In Millions, unless otherwise specified				3 Months Ended			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Trading Liabilities Structured Foreign Exchange Swaptions Option Pricing Model	Mar. 31, 2013 Trading Liabilities Structured Foreign Exchange Swaptions Option Pricing Model Minimum	Mar. 31, 2013 Trading Liabilities Structured Foreign Exchange Swaptions Option Pricing Model Maximum	Mar. 31, 2013 Trading Liabilities Equity Options Option Pricing Model	Mar. 31, 2013 Trading Liabilities Equity Options Option Pricing Model Minimum	Mar. 31, 2013 Trading Liabilities Equity Options Option Pricing Model Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair value of liabilities	$ 170	$ 224	$ 115			$ 55
Correlation risk (percent)				0.00%	25.00%
Volatility (percent)				11.00%	16.00%		22.00%	28.00%