Fair Value Measurement- Quantitative Information about Level 3 Fair Value Measurements of Assets (Detail) (USD $) In Millions, unless otherwise specified							9 Months Ended							9 Months Ended						9 Months Ended
	Sep. 30, 2014 Fair Value, Measurements, Recurring Level 3	Dec. 31, 2013 Fair Value, Measurements, Recurring Level 3	Sep. 30, 2014 Fair Value, Measurements, Nonrecurring	Dec. 31, 2013 Fair Value, Measurements, Nonrecurring	Sep. 30, 2014 Fair Value, Measurements, Nonrecurring Level 3	Dec. 31, 2013 Fair Value, Measurements, Nonrecurring Level 3	Sep. 30, 2014 Securities available-for-sale Fair Value, Measurements, Recurring Level 3 State and political subdivisions Discounted Cash Flow	Sep. 30, 2014 Trading Securities Fair Value, Measurements, Recurring Level 3 Structured Foreign Exchange Swaptions Option Pricing Model Minimum	Sep. 30, 2014 Trading Securities Fair Value, Measurements, Recurring Level 3 Structured Foreign Exchange Swaptions Option Pricing Model Maximum	Sep. 30, 2014 Trading Securities Fair Value, Measurements, Recurring Level 3 Long-Term Foreign Exchange Options Option Pricing Model		Sep. 30, 2014 Trading Securities Fair Value, Measurements, Recurring Level 3 Equity Options Option Pricing Model		Sep. 30, 2014 Trading Securities Fair Value, Measurements, Recurring Level 3 Equity Options Option Pricing Model Minimum	Sep. 30, 2014 Trading Securities Fair Value, Measurements, Recurring Level 3 Equity Options Option Pricing Model Maximum	Sep. 30, 2014 Loans Receivable Fair Value, Measurements, Nonrecurring Level 3	Sep. 30, 2014 Loans Receivable Fair Value, Measurements, Nonrecurring Level 3 Minimum	Sep. 30, 2014 Loans Receivable Fair Value, Measurements, Nonrecurring Level 3 Maximum	Sep. 30, 2014 Loans Receivable Fair Value, Measurements, Nonrecurring Level 3 Discounted Cash Flow	Sep. 30, 2014 Loans Receivable Fair Value, Measurements, Nonrecurring Level 3 Discounted Cash Flow Minimum	Sep. 30, 2014 Loans Receivable Fair Value, Measurements, Nonrecurring Level 3 Discounted Cash Flow Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value of assets	$ 114	$ 139	$ 129	$ 152	$ 5	$ 9	$ 11			$ 18	[1]	$ 6	[1]						$ 5
Fair value inputs, expected credit loss (percent)							4.00%
Correlation risk (percent)								0.00%	25.00%
Volatility (percent)								11.00%	18.00%					21.00%	25.00%
Timing of sale																	0 months	12 months
Cap rate (percent)																8.00%
Cost to complete/sell (percent)																				0.00%	40.00%

[1] The option pricing model uses market inputs such as foreign currency exchange rates, interest rates and volatility to calculate the fair value of the option.